This is my ultimate dream build, of which I now have EIGHT examples. Previous plans for four have... uhh... yeah.

The genesis of these race builds is that I'm looking to be able to run multiple identical quads, and get extremely comfortable with their performance at the limit. Running higher quality parts is intended mostly to get maximally consistent performance more than trying to extract more from the quad in race conditions.

Frame - This frame is one of the best out there, the FPV-FlightClub Neutron-R. Thoughtful design, and there's a reason pilots like CaptainVanover choose this frame. Dedicated 20x20 stack mounting, available in my preferred Hybrid layout (5" Stretch-X front, 6" True-X rear), which is a really outstanding handling setup.
The canopy on offer from FlightClub is a TPU unit, which looks pretty stunning with the sharkfin - and is arguably superior in the V2 flip-stick configuration. In tall grass the shark fin is less useful, but the flip-stick setups allows combining the aethetics of a MayDayFPV design with the better aero and turtle-mode capability of a flip-stick. The included TPU antenna mount pairs excellently with the Unify type SMA pigtail, and if you solder up the ESC capacitor the way I have here, it actually locks snugly in place and protects the whole setup perfectly.
I do get to claim hipster status on being one of the first racers running hybrid geometry frames and suggesting to faster pilots to give it a shot, but this is one of the best implementations of that frame geometry.

FC - The flight controller is worth a mention - an F4 in 20x20 mounting is always a great answer, but the newest Talon F4 combines a Pin I/O Pit Switch along with Blackbox capability, which are my go-to capabilities for a race build. If I can make it out to any larger team races, this is a must-have capability, although practically it's actually a great thing to have all-around on a build since there isn't any extra complexity involved. I have a few with cheaper FC's (Omnibus Nano F4 v7, and iFlight's Succex-E 20x20), which perform the same, but require the addition of a pit switch to get the same functionality, and both of these give up half the blackbox storage space, which is actually a noticeable limitation.
I can't see a reason not to go with the Talon F7 with MPU6000, or F7 Dual, rocking the same features, and being absolutley future-proof. When these happened to be on sale at PyroDrone and FPV FlightClub, the price was too good to pass up. Performance running 4k/4k/DSHOT300 is still absolutely phenomenal.

ESC - the Aikon2020 is the choice. Really any 32Bit ESC configured with Rampup/Startup Power down a 0.125, Demag Compensation High, Motor Timing to 22° is going to be incredibly resilient, and remarkably efficient. Longevity for ESCs is all I care about, and the form factor obviously needs to go well with the frame, which these both do. Again the 6S 25A rated version for budget reasons to stay under $250 but still get the overall performance I'm after. I have cheaper versions running the Ori32 with the same 25A rating, and iFlight Succex-E. The Ori32 happily plugs along with those BLHeli_32 settings, although I'm convinced the reason it's surviving well is that I have that paricular one on 4S. The other cheaper ESCs are all BLHeli_S, and have since been updated to JESC - basically can't tell a difference, because both are incredibly smooth. Practically at the AUW I'm achieving these are going to unload extremely well. With the rampup power and motor timing adjusted, and using the DMin capability of Betaflight 4.1, electrical and heat stress on the ESCs is totally manageable.

Motors - These motors are more than just gorgeous. SpitfireFPV had the foresight to bulk order BrotherHobby R6 2207 motors a year ago, and those are honestly the best motors for what I was seeking to achieve with this build. Really smooth, excellent power, and the weight is actually impressive for just how much stator and magnet they bring, and importantly have that excellent meat-hammer top bell surface to limit propeller slip. While the outright power delivery from a 2207 isn't the absolute highest, they are extremely light and deliver the efficiency I want for the batteries & props I like most. I'm sure I could run 2207.5 or 2208 motors and get massive top end power, but that isn't where I feel like these setups are lacking, at least with me on the sticks. If I decided I needed more top end, the SunnySky EdgeRacing 2207.5's hold that crown for maximum power delivery, but at a 3.5g per motor weight penalty. If left to my own devices, I'd run those ER2207's on 30x30 frames, and these R6 motors on lighter 20x20 stack frames.

Propellers - I've actually switched to running these primarily on the Gemfan 51466 props, along side DAL 5145 Cyclone. I'm still partial to DAL's V2 Cyclones, liking the T5046C on race days because of the extreme durability. I do really like T5249C's, Gemfan's 51499 and 5149 props, and on occasion the T5050C and B5050C props for wide open tracks. Each of those alternative props have one trait that puts them over the top, but those V2 Cyclones are just the universal 'B' student that are very good at everything, and the most durable. I totally agree with more savvy reviewers that other props perform better in the air, but for how much I battle it out with gate hardware, that's what I need.

RC - Me personally, I like running FrSky XM+ receivers, since they aren't generating potential EMI with telemetry. I only care about RSSI, which just requires a quick reflash, running the RSSI Aux Channel in Betaflight, and toss that in the OSD. The biggest upgrade to this, for those flying a Taranis, is actually updating the OpenTX firmware onboard - the latest build seems to have fixed the inconsistent and excessive latency on everything due to heartbeat mismatches - seems to have fixed that bug, and cleaned up the Betaflight channel response smoothing quite a bit.

Camera - My preferred camera is the Foxeer Predator. I actually like the look of CMOS cameras, and the FOV on 1.8mm lenses for these works perfectly for going fast in all the light conditions I encounter. The V2/3/4 all perform basically the same to me, so I run what I have in Purple. I do really like the solder-lead variant for tight builds, and even on these I'm a really big fan, but the normal setup works great too.

VTX - This might be a bit odd, but these run the Eachine VTX03S. Yeah, Eachine. As an alternative video transmitter, the AKK FX3 and Eachine VTX03S are among my favorites. I have a handful of defunct Unify's, but have yet to kill one of these. I like these the most out of the cheaper options because they're the smallest and lightest in a solid mount-able configuration. I'm beginning to think that running VTXs off 5V regulators is probably the real key to longevity, but for that level of effort I've been extremely impressed with the $10 VTXs. The AKK Race VTX perform similarly if you want MMCX plugs, but lacks a truly useful channel indicator that the VTX03S brings - but if you're happily using SmartAudio, then it's actually pretty solid. Mounting these is the real challenge, but as long as they're not vibrating directly on top of the MPU, it works to VHB tape them down to a solid surface.

Antenna - The lollipop antennas are a fantastic value - I still wish they'd offer the Stubby SMA version in purple, but taking matters into my own hands with spray paint is working just fine. I actually like the worn look of the antennas after some use, so that battle-worn rattle can job is good enough for now.

Firmware & Tuning - Betaflight 4.1 has been the answer, and is worth moving past 3.5.7 to me. Adding BLHeli32.66 (or 32.7)and Bidirectional DSHOT capability (RPM Telemetry by packet sent over the motor command signal wire), that enables RPM filtering has worked extremely well for me - absolutely dialed. The tuning window is a bit different - I've used the sliders to set ratios that are, to me, very high P/D values and DBoost from DMin. The biggest change is actually reducing the I term gains, and Antigravity strength, which I never imagined I'd have to do, but it seems to have sorted the last little bit of seeing 'bumps' under high-G loading. High FF values just make it track setpoint even better, so that produces the closest feeling I've ever felt to the quad being an extension of my neurons. Really insanely good.

Batteries - I tend to run ChinaHobbyLine batteries. The massive sales are just too good to ignore, and I'm happier with a big pile of batteries that perform very well, instead of a handful of batteries that might perform slightly better for a couple dozen cycles. The White Series 100C and Black Series 100C batteries have been my outright favorite for performance and weight.

Weight - These all happen to fall between 298-304g dry weight, and with the batteries I run (167-225g) that puts me in the 475-525g weight class, which is actually quite good for 2207 motors hauling 1500mAh batteries. I actually prefer running the lighter configurations that put me around 475g, and with the efficiency of these motors and my personal inability to leave the throttle stuck to plastic for a full two minutes means I still experience zero sag for any MultiGP type racecourses.

As far as budget, I was able to get these four built for a fair bit less than you'd expect, which is awesome. One-off closeout sales, and the patience to wait across four months while building these plays a huge role... saves about $100 from what RotorBuilds tends to show for these parts.

If you're looking to build a clone of this, I would probably run this Neutron-R frame, R6 2207 Motors, Predator V4 camera - worth bumping up to the full-on Talon F7 Fusion Gigawatt stack, and move to the UnifyNano VTX, AXII, and obviously CRSF Nano for control link. I'm not unhappy with the cost savings measures I've applied to these, but having 8k/8k bidirectional DShot on F7 boards while running all-TBS radio hardware and Stubby AXIIs is the only major improvement direction I can think of.

If you're wanting a more wide-open-throttle variant of these, I'd move to Proton-R with beefier 30x30 stacks, and run the SunnySky Edge Racing 2207.5 motors. Heavier overall, but the thrust on offer from those 1850KV motors is absolutely massive (see MiniQuadTestBench), and also happen to be remarkably cost-effective.

If you want to build something with comparable performance on a much tighter budget, building a Floss3.0L on an iFlight SuccexV2 20x20 stack, EMAX ECO 2207 Motors, and running otherwise similar parts will get you to insane performance at a nearly untouchable price point.

If you're curious about these alternate builds, there is also this reference Google Sheets document I maintain here:
https://docs.google.com/spreadsheets/d/1jnR4JIQM72z0eItMZe-0KEGYw_0bsV0hiUvK3h_cUiE/edit?usp=sharing