You can never overpay for a QB if he can help you win. (Eli Manning is the perfect example)
Cutler's record has alot more to do with a lack of defense then what he was doing where as the Bears QBs records had a lot more to do with lack of offensive production.
I have heard more then one annalist say that when looking at the Bears film last year, there were a lot of WRs running open down the field, but the Bears QB couldn't get the ball to them. Well Cutler can get the ball to them. Then, either the Bears get big passing plays or defenses will have to pull off them which opens up more space to run.