[narwan]

"On the other hand my point was made even by your tests that after full movement a 1950s era T-10 still had the same ROF as most of the Abrams on the field"

Now lets turn that back into 'reality'. Shouldn't both vehicles have 0 shots after using their full movement? After all, they either just spend the entire time allowed for a turn 'moving' leaving no time left for firing at all, or if there still is time left (to fire), they should be able to move faster in a turn (using that time to keep moving instead of firing).
But that's not how the game works. As in any model of (part of) reality abstractions need to be made to simplify things. Otherwise you wouldn't have a model but reality itself. A good model distinguishes itself not by it's processes (what you seem to be focused on) but by it's outcomes. For instances, the game makes no distinctions between KIA, WIA (physical or otherwise), MIA, POW's, and deserters. It has only a broad category named 'kills' (with the occassional 'group surrender'). Works fine because for the model it doesn't matter how the enemy troops were taken out of the fight, just that they are.
Same with your ROF. The real question is whether an accurate balance of fighting power is achieved, of which the ROF is only part.

You mention 2-part ammo as a factor for ROF, well, speed is also a factor; the faster a vehicle is moving the bumpier the ride and the harder the task for the loader. At the end of the round the Abrams is moving much faster than the T10 (if both use their full movement) so it's loader should get a bigger penalty than the T10's loader, shouldn't they? Would that penalty be bigger, equal to, or smaller than the 2-part ammo penalty?