Now I think that KV-8 is superfluous. I want to tell you about the SU-76M. It has an open cockpit. According to my idea, SU-76M has a weak armour, but all-5 effectiveness against all types of enemies and can do an artillery salvo (for a price). SU-85 is a classic tank destroyer. T-34-85 is a tank having a high effectiveness against tanks, but the standard 5 against the other goals, and after some update can carry infantry.
So:
SU-76M - light armour, normal fire-power vs all + arty,
SU-85 - medium armour, good vs tanks,
T-34-85 - medium armour, good vs tanks + normal vs all other. (it is like up-gunned Shermans)