I've been messing with this copter for a few months now. The biggest setback has been ESC issues with KDE 2814XF-515 motors. Doing it over again, I'd bite the bullet and buy the $$ KDE ESC's made specifically for their motors.
After 4 different ESC's (3 SimonK) tried, the HobbyWing 40A OPTO XRotor (non-SimonK) seems to be the best, and also increased the flight time. The KDE ESC's would be even better I'm told.
Choosing the right prop configuration was also a problem since this is not a kit build. After trying several different props, it now has 15x5.5 Tarot TM on the bottom and 14x5.5 Gemfan TM on the top. As others have discovered, the pwm disparity from top to bottom caused stability issues and requires more customized PID's. Switching to this latest setup appears to have taken the Auto Tune results better and the Yaw IMAX and Loiter P/I Rates are back to default. There's still more tuning needed, but I like the why it flies much more already.
PWM at hover and some flying with 15x5.5 top and bottom (10 mph wind gusts):
PWM at hover with some flying at end with 15x5.5 top and 14x5.5 bottom (10 mph wind gusts)
Thanks do Doug and others who suggested changing the top 1" smaller.
The other day I received a Neo-M8N GPS from CSGShop and installed it. No more waiting for <2 hdop, or cancelling a mission because of GPS glitches, and now have redundancy to boot.
The best hover time achieved so far is 23 minutes (to battery FS 14.0v/3.5v min cell) using a Multistar 10000mah 10c battery. I think it will get better with warmer temps and more fiddling, but for now it actually beat expectations. Next will be trying 2p batteries to see how it handles.
Here's the copter minus the 2nd GPS and waiting for wiring harness loom for the new one. AUW is 3.1kg