Part of the reason the planes become so unstable it's because the code auto corrects itself in the vertical axis aggressively.
There's nothing wrong with how the plane would fly if the Rudder auto correct feature could be disabled, optionally of course.
This is probably not news to many but I would request this to be looked at just as in the recent patch some analog features were added for analog control of throttle,albeit it doesn't work quite right.
I would suggest to take a look at this , and maybe it would fix the high speed woes of all the planes.