I have owned nothing but the KK2.1 boards since they came out. Always flash it with this site. http://lazyzero.de/en/modellbau/kkmulticopterflashtool
Since the last 1.9 version I don't ever have to change the P gain or I limit on anything with a 935kv motor. Or with a 430mm frame or bigger. I just fly them with the default settings. 65/30. I think. Yaw I like it a little lower than default. I do like my stick scale settings at 10,10,40. Yaw is always good to have incase you need to turn quickly while learning.
Now I have found on the "Black bug" which I would call an indoor model/outdoor model, I do have to lower the P gain to 20 and the I limit to half of that around 9 or 10. Seems it likes it best around this setting for that setup. That uses 1050 kv motors. Steveis is a genius for writing that firmware.
My skill level is newbie to just touching intermediate. I can fly in a circle with the nose facing the front way. Any faster I will crash it. One day I hope to get to FPV racing level with my goggles. But that's a ways off.