I've heard the max expertise possible in the game is 1380, here is a formula list
that will show you what your expertise does.
At 1150 you get - 22.02% bonus damage, and 18.05% damage reduction.
At 1340 you get - 24.59% bonus damage, and 19.74% damage reduction.
So . . . compared to someone with 1150, you're at least at a 4% difference (because of the extra damage you do, and the damage increase in damage reduction). The real question is if you drop that expertise is what you're getting going to make up for that difference.