So, my Quad has a KK2.1.5 board, Hobbyking Blueseries 20A ESC's and 1000kv Motors.
With stock firmware on the KK and the ESC's it flew, but was very twitchy, even after tuning the PI settings.
So I decided to flash the Steveis KK2.1.5 Firmware (v1.17S1 Lite). After that, it flew a little more...