Just to point out something - there's a Canon 70-200 f/2.8L non-IS that's in that price range, as well. 
The f/4 with IS versus the f/2.8 really comes down to what sort of things you'll be shooting and what weight you're willing to carry. The f/2.8 non-IS is also a bit more tolerant of teleconverters if you feel you may need more reach in future.

The f/4 with IS versus the f/2.8 really comes down to what sort of things you'll be shooting and what weight you're willing to carry. The f/2.8 non-IS is also a bit more tolerant of teleconverters if you feel you may need more reach in future.