I used to covet the motorized Tamiya kits back in the 1970s. My friends and I would conduct "tank torture tests" in the backyard. We would dig up the dirt, make obstacles from pebbles, create mud puddles, then run each of our models through this grueling course to see who's tank made it across the finish line! There were all manner of accidents, like thrown track, grass/mud buildup in the running gear, and short circuiting motors. The all-time champion was my friend's M41 Walker Bulldog, which flew across the battlefield like the wind, never threw track, and even ran underwater! Heady days! Then there was the "ballistic test range" for our retired tanks, but that is another story.
Regarding the new Tamiya Mark IV, I don't think it runs at the advertised "scale speed", as the model moves way too fast. Didn't the real things cross the battlefield at something like 2-1/2 mph? I have seen the kit in the flesh, and it does look very nice.