Most tamiya tanks are close to the same speed save the modern tanks and the ones that have geardown hubs.
one way to tell is go download the manual for the tank you are thinking of amd see if it has the same gear boxes as the sherman. Those are standard and probably the same as your p4.
The sherman is quite fast at a scale 22 mph which is top speed on a flat raod for that tank any way. Combat would be unter 10 most of the time. At a field like danville you probably dont want fast any way. MAny people gear down with after market trannys to get lower speeds ao they can keep crawling on those last few hits rather than get bogged down.
on our huge open field in san diego speed is a benefit but after a few hits, your barely moving.