I'm not 100% sure, but I think its the same boddy with smaller arms. So I can probably get larger arms and make it 5" :D

Yessir you are correct! Just an arm swap will make it accept 5" props. I run the same exact electronics, except for motors. On my 5" I'm running the NBD Flow 2004 1750kv. Which is pretty perfect for 6s with a 5" prop. I wish I could swap them for the 1850kv ones though, just to get a hair more rpm with the 4.5" prop. Then run a 5-10% throttle cut when running 5" props. But yea, even on 1750kv the 4523 props are awesome. Just makes for an even zippier setup. It's definitely worth trying!

how are the Flow motors? they are really good priced.

They are AWESOME motors.. I was actually turned off by both how cheap they were, along with how many people were buying them. I know, it's dumb.. I just wondered how good could they be if they're this cheap? and people are probably just buying them because they are the cheapest 2004 available (at the time.) I ended up buying the 8 pack when they were available for $100, and they have been so rock solid. They have boatloads of power on a light 5", and they're efficient and tough. I drove my first 2fiddy face first into the ground, broke an arm, and the motors and wires held up great. I wish that deal was still available! Also running the Tmotor 2004's on another build, and they are awesome too.

Those flow motors are the toughest 2004 motors availble. I bought 4 or 5 different 2004 motors and all of them were damaged way to easily. the NBD ones are great, but for 4" I use 1804s which are better for power to weight, and swapped my 5in 2Fiddys to 2104 or 2105.5s.

Have you tried the 4.5" props on your 5" 2fiddy? If not, you gotta try it out. Super fun!

I've tried quite a few props and motor combos on 4-5in 2fiddy frames. I find the Pb&j props the best for my preferences. Insane thrust and efficient cruising.