Today I just raised a Berserker to 20 and rolled his perks 4 times. Now he have +15 VIT, +15 VIT, +10 STR.
Too bad he had sh*tty stat grow on his level-ups. 36 STR, 47 VIT, 20 GRT
So in 20 levels he gained 21 STR, 17 VIT and 20 GRT.