Global illumination - High vs Ultra? Anyone could provide comparison?

[Alleluja2000]

So GI + shadows looks great but on ultra is tanking my performance to mid 30s while on high it's rock solid 60fps.
So what's the difference in image quality? Is GI + shadows on Ultra really THAT much better looking than on high?? Anyone could provide screens from some areas further into the game (as I just started the league)