Just in case, you did not hear about simonk firmware for ESCs (or if you simply have not tested it) yet:
I gave it a try today and changed my Mystery 20A ESCs from goodluckbuy against flyduino Simonk ESCs (already flashed).
The copter was so much more stable and precise to control. I also was able to increase the values of my flight control without any oscillation.
Thanks to Schachti for telling me to try simonk ESCs 🙂