Being realistic, in any tank in a combat zone, a speed of 15-20 mph max was pretty much the norm, with convoy speeds actually slower. With many tanks, like Tigers and KTs, that was top out, unless one got onto a straight, slight downhill grade. Even a Sherman, rolling on a downhill grade can pick up some pretty good speed. A few tanks like the Stuarts, M-41 and M-18 TD could boogy out faster, but they were designed for it. Early T-34s had a reputation of being fast, albeit they took two men to shift and Russians were not after tank longevity but superrior numbers to overrun the Germans.

Cross country in soft ground or loose gravel and keeping your eyes on the woodlines, keeping your infantry with you etc, speeds were normally closer to 5-10. Short spurts of 30+ or so were possible on some tanks with better engines, but higher speeds tended to put way too much stress on the engine and in a combat environment, having an engine getting tummy cramps in a delicate moment is really not cool. [:'(]

Generally a road speed of 20mph and cross country of about 10 would put you in a good actual speed for about any WW II tank.
Now if you take the Abrams, that's a totally different world[X(] M-41 could click along at 40 and top out at 45 mph. [8D]