The difference in speed for these tanks is utterly negligible.
T-34/76 is 6.5, PzIV is 6.3. There's the same 0.2 difference is acceleration and deceleration. It's really not much at all, not nearly enough to make a difference when you consider the Rate of Fire the PaK has.
The T-34/85 is actually slower than the panther (6.6)
Most american tanks are also 6.5. Most tanks barring the tiny or massive ones all go about the same speed.
Oddly enough, the max speed for a KV1 is 6.7. Good luck getting it to go that fast, mind.
Pak is definitely superior to the Zis in AT, never said it wasn't. T3476 accelerates faster too, and more importantly costs about 20% less for exactly the same survivability against an AT gun as a P4.
T3485 is the best medium (except maybe the E8) because of it's 800 health, among other very decent stats. Panther is in a different league cost wise and doesn't bear comparison (tank hunter, useless against AT guns anyway, and a general waste of resources in a 1v1).
And the max speed of a KV1 is actually 5.1. It has 270 armor and 800HP though, so it bounces shots decently well and can survive the ones it doesn't deflect.