Here is elric stats per lvl based on stars
http://soul-hunters.wikia.com/wiki/ElricSo going from 2 to 3 stars will give you 19 extra health per lvl, 1 physical attack, and .4 magic resist and armor. So at lvl 40 getting the 3rd star is an increase of 760 hp, 40 attack, 16 magic and armor. From 3 to 4 you get 18 hp per lvl, .9 attack, .5 magic and armor. At lvl 40 that's a total of 720 hp, 36 damage, and 20 magic and armor.