Just a few thoughts based on my experience and measurements....

1. As you push velocities into the transonic region (over Mach 0.8-0.85 ie 900-950 fps) accuracy often suffers due to buffeting....

2. As you push velocities into the transonic region the Ballistics Coefficient (and hence the wind drift) suffers....

3. At a velocity of 950 fps, the FPE is double the pellet weight.... Unimportant, but it makes for an easy calculation....

I use 950 fps as my "speed limit".... If the gun is capable of exceeding that, I change to a heavier pellet.... and ultimately a larger caliber....

Bob