Having now tried out both heavy lines as far as the IS7 on Russian side and Maus on German side im now qualified to say the following.
I LOVE MY IS.
Ive got rid of all my high teir heavys and kept my IS with the 122mm cannon, ive added a rammer, spall liner and Binocs (10% extra view range) and it rocks. even when i lose i rarely make a loss. With premium i make a good profit on most games.
Attached is an average example of what I make per game now. Dam fine fun
WIth the 122 u can damage most things with a hit. I get very few bounces using manual aim and some quite supprising results.
I hit an IS7 in the side armour yesterday, set him on fire and blew him up in 1 shot..