I know this topic has been dormant for some time but thought it would be better to say here that I play with heavy tanks on a cost: 7/ att and def: 4 basis but with a move of just 1.
I like to keep house rules ruthlessly simple and eliminating the suggested heavy tank non combat move of 2 also helps to ensure the unit doesn’t become too overpowering. (Also helped by the fact that I also play with heavy artillery on a cost 5, att/def 3 and move 1 basis so both attacker and defender have access to a unit with +1 hit for +1IPC compared to OOB).
:-)