I think there is some confusion in this thread. "Fast tanks" (i.e. tanks with a high top speed say 30mph for example {compared to "slow tanks" say 10 mph don't necessarily make for "fast divisions"). The speed of a division movement has more to do with other parts (is infantry motorized or mechanized), is the supply system able to keep up, what is the terrain like (hard to speed through forests in any vehicle) what is the density of roads (mechanized infantry and tanks can move easily off road in open terrain but motorized infantry, towed artillery, supply and refueling vehicles are much more road dependent and oh by the way how often does your tank "break down" and need maintenance help. The other thing is that even if you have slow heavy tanks and you have good roads or railroads plus tank transporters these things can be moved fairly quickly.