I wanted to say that someone should check what happens with stats multipliers on girls on 4/5 stars, but it seems to be just expansion of old system. AKA 1-3 starts were a static 1.3 to 1.9 (0.3 jumps) multiplier. 5 star 40 level Bunny is 310 Hardcore which is 2.5 more than wiki says she is on zero stars, which means that 4/5 stars just expand that to 2.2 and 2.5 multiplier. 5 star bunny is barely better in HC stat than Nika lol.
EDIT:
On a side note, I manged to hit 42 on main account - got 50 more upgrades - so the 50 upgrades/level till level cap seems to continue to be true.