The innate regen bonus for high levels appears to be INT(level/10) + 1.
Level 11 Erudite wizard with no effect gear and no AAs whatever: innate regen of 3.
Level 70 Barb shaman with Innate regen 3 and no other regen AA, removed all gear: innate regen of 12.
So the cap is indeed 45 with those additional modifiers in mind, thanks for the input from all.