Supersonic = Mach-1 ~ 1,130fps at sealevel STP
The reason you don't want drop below s/s in precison shooting is that dropping through the shockzone perterbs flight. You either want to be definitely sonic or definitively supersonic -- but not "trans"sonic right at the target. (Then you don't know what's going to happen.)
Here's the exterior ballistic for an AMax starting at 2,300:
(If you bump muzzle velocity up to 2,550, you push that remaining 1,200fps/supersonic velocity out to 1,000 yards)