Have to bear in mind that the books listing top speed of a vehicle are relating to official military test results and generally under ideal conditions. In the field with weather, road, track type and additional loads effecting the vehicle, the actual field speeds are considerably slower. The Pershing is supposed to run at 25 mph, bit with its weak Ford engine, if you ran it over 20 for any length of time, it would be sitting off the road blowing steam out the radiator and most likely changing a set of 16 fan belts. The Shermans with radials could click along at 35 when they got wound up and running full out, but given top speed was normally around 25, depending on the particular model. The M-46 was generally given 30 mph, but 20-25 was a good speed, when all 12 cylinders were cooking.