On the KV-4, I use the classic Vents (in bonus-slot), Vstab & rammer setup, but mainly because I got used to that setup. Been thinking of switching the Vstab to the IRM, to help with the abysmal turn rate. Rammer & vent combo brings down the 107 topgun reload within permatrack territory of several tanks you face.
With KV-5, I switched from vents, rammer & vert stab to Improved Hardener, Improved rotation & turbocharger + Speed governor remover in consumable slot (works as a sort of 4th equipment slot for KV-5), so it can throw its weight around on the med flanks & won't get tracked easy.. Likely not the best build, but fun to play a speedy armored tank with ramming power.