Do you really believe the M3 is faster than 250/251 in cross country performance ?
Values are road speed.
I'd actually give the -251 an edge in cross country performance thanks to the larger tracks (lighter footprint), and tighter gear ratio (low RPM performance). Ultimately, they were not that much different (gross weight, engine hp/ton, cargo capacity, armor, etc). The biggest difference is in their road speed which is fully exploited in AH.
If HTC were to somehow have 2 top end speeds (road and cross country), the usage between the 2 troop carriers would be much more similar.
Speaking of which, the next topic could be how to add in a road from the spawn point to the town to the field, and give vehicles with typically more road use than not (jeep, M3, -251) their road speed and when they are not on the road they get their cross country road speed. There would be two major issues with that: what to do with the tanks and HTC would have to figure out how to get their truck convoys transparent so they wouldn't plow player controlled gv's off the road. OR.... better yet, add in a road from the gv spawn points to the town and field that is not associated with the convoys.