I played a bit on both easy and very hard. I can't be sure, but I think the random mods on very hard are better. Like I just bought a green ring off the shop at level 11 on very hard that adds 17 ice damage, while my character on easy hasn't seen anything nearly as strong even at level 16.
+24% of 60 DPS (at level 11) is a hell of a lot less than +17 damage with a fast weapon.
Anyway the highest +% of any kind of damage I've seen so far up to level 20 is +7%. Though I also haven't seen anything nearly as good as that ring I mentioned, so maybe the game is spitting out freak items occasionally.