I never had it when it was t6, I'd think it would have been better then, though. When it was moved up, all it got was a bigger engine and more HP, right?
I want to like the kv3, but I just can't. Anyone t7+ that isn't a complete moron will pen it pretty reliably. I know there are plenty of t6s that can do that too, like the kv1s, but it isn't as common and I think the t150 will be more competitive within its own tier since its hull is shorter, side armor is just as strong as the kv3's, and it is faster. Alpha isn't nearly as good, but it is still pretty nice for t6 and the RoF is also pretty decent.
I've never played the t150, though. I unlocked the kv3 before the t150 was in the game. It looks really good on paper, though, and it won't get t9s 2/3 of the time like the kv3 normally does. Even if it is equally cursed with t8s, I shouldn't ever lose money with it, and I would rather face t8s in a t6 than t9s in a t7 anyway.