I tested the tanks for acceleration to 20mph when the shifting was manual, the Panther won out in a major way. The T34's were the slowest.
I tested to 20mph and I tested to max speed. The Panther could get to max speed (29mph) faster than the Panver IV and all three M4's could get to max speed (25-26mph). Against te T34's, the Panther had an easy jump. It actually took a decent amount of time for the Panther to get over taken my the T34's from a stopped position.
I dont have historical data, but it would seem to me that the shorter gear span/ration would allow the Panther to harness the power of the engine better and get the engine power tranfered to the tracks better than anything else. I wouldnt doubt for a split second that the Panther had the best acceleration speed for a 25 ton plus tank in WWII. That is just a hunch, though.