I would stick with a RB pick first round. I'm drafting 11th in a 12 team league this year, and right in that ballpark you've got guys like Henry, Maroney, Bush, McGahee...all who have upside. In my league last year, Steven Jackson went late first round, Brian Westbrook early second and I picked up Gore in the 4th.
Stick with the RB pick. It won't be wasted unless there's an injury or some trype of major, offensive meltdown (ala LaMont Jordon), which could happen to any player.
As far as QBs, the top ten definitely won't be gone before the 3rd-4th round, unless you can start 2 QBs in your league or you're in a 16 teamer, and even then.... Hell, Bress and Palmer could be there. Palmer went 3rd rd in my league last year. If you're very eager to grab one, you can still get guys like Hasselbeck, Romo, McNabb and Kitna easily, even if there's a mad dash run for QBs.