What "airspeed" is the airplane's maneuverability, control and stability based on?
 

From my understanding, at high altitude and high speed where EAS is significantly different from CAS, the airplane's maneuverability, control and stability would be based on a speed that's actually in-between CAS and EAS, but very, very close to EAS.

If you have articles or equations or reports that prove the answer, please include them!

I don't understand what you are asking, exactly.

Stability, Manoeuvravility and Controlability are related to many variables, no only speed. For instance, manoeuvring stability varies with TAS.

I agree with Microburst2002.

Perhaps these lecture notes will help you:

Lecture notes on airplane stability and control I: Part II :: TU Delft Institutional Repository

Lecture notes on airplane stability and control I: Part I :: TU Delft Institutional Repository