I think KV-3 is oft underestimated by most players. The front is disgustingly bouncy and aiming for the turret is the same. The move up to Tier VII is a good one overall, considering it gained much needed hp with a better engine upgrade and an equivalent gun to the IS.
That said, I'm also surprised by how well T25/2 is doing. For a tank destroyer, it plays so much more like a gimped medium than a proper TD.