I'm "building" the same type of quad but a sight seeing machine, not a race quad, as I need at least 7 min flight times and want 10 min like a geared quad provides on 1S @ 750mAh so wishing a verity of 4.5 inch props were available for running on 2S as 5in is too big for a small frame and 4in is too small for pumping air slower and keeping the drag down as Blade figured out on the 200QX. I'm using Sunnnysky 1306S 3100KV motors and they seem to like 2S best so will stick with 2S on this build as I change frames and ESC's again as better ones keep coming out. This movement is what was needed for public safety flying quads FPV and there is no reason a small quad cannot be both fast and fly for longer durations. And IMO needing a rigid carbon fiber frame that blocks RF in place of quality reinforced plastic that can put the center of mass in the ideal location and do other things a mold allows like running wires through it shows these small quads paying attention to weight are just in their infancy. My geared quad is hardly maximized for weight with it's large FCB but with a 1.3 Vtx and 4 gram camera is well under 120 grams and I get 10 minute flights where hovering in front of a large screen monitor shows the same vibration free image as when the motors are not running... using bushings as well as bearings, so that's one fallacy of geared quads to ditch.
These carbon fiber frame builds are heavier than needed IMO and I think we will see FPV builds approaching 50/50 battery to weight ratios using better composites. I got close if not over 30 hours on a set of 7mm coreless brushed motors I picked out used on a JJ1000 showing high quality coreless motors (not available yet, I had to pick these 4 out of 16 motors) are not as bad as some think so there are lots of options to make a super fast small lightweight quad for FPV. The RMRC 4in1 ESC is a step in the right direction but not the only direction as DC has its advantages as well when things get smaller. If you could just clean out and lubricate the coreless motors in use as the brushes wear you would see an increase in operating time and better performance. I paid $10.50 for the JJ1000 on sale for the backyard at night so that shows what that level of performance can cost giving 7min+ flight times @ 50% full throttle with the lights on.