I've made some modifications to the previous version of my take on the Calimero from Dave_C. The previous version was stretch x with a motor to motor distance just large enough to fit the electronics. The stretch x frame weighed about 10.5g with 3 walls, 30% infill, and 5mm thick.

changes to this version....
-This frame is more of a true x. I didn't shorten the distance back to front very much. Instead, I widened the arms about 3mm on each side. My goal was to provide more stability in the corners and to give better airflow off the propellers. In addition, it wil be a lot easier to fit a eos2 or similar camera if I want to.
-I added mounts for the FC so now the FC has 4 mounting points instead of 2.
-This version seems more stiff than the previous version despite there being a hole for the FC mount in between the two rear arms.
-Currently, I have the full 5mm thickness around the motor mounts. The previous version was 5mm thick arms, but 2.5mm thick motor mounts to save weight. I may change this in the future since I didn't have an breaks at the motor mounts on the previous version. However, I don't have any more m2's at the moment for a 2.5mm motor mount so....
-This version comes in at 12.2g with 3 walls and 30% infill and 5mm thick.

I like this version more than the previous version. I think having 4 FC mounts helps with the tune, but also make the build more durable (by holding the FC in place more securaly if crashed) and has a "finished" look to it. In addition, the more "true x" design seems more comfortable to me in the turns.

NOTE: . In my experience, I have had a few breaks near the rear standoff. I feel this version has more material around this area and I am hoping for it to be more robust. However, overall, it survives crashes as expected. It's not as strong as carbon a fiber frame, but it's not weak either.

Build is a transplant from the previous version with the crazybee fc, 1202.5 6400kv motors, 25mw aio camera, and gemfan 3018 props. about 54g dry and I use 450mah 3s lipos.