As a warrior I didn't bother with the Know Creature skill, but would guess the highest creature level is around 50.
I maxed Survivor's Instinct when I got the wastelands (level 50) just using up some spare skill points, and it was pretty much the only healing I required for the rest of the game (I used 3 minor restoration potions total, in 2 of the main fights). Even the group of 4 or 5 dragon riders couldn't do much damage, despite freezing me a couple times.
