I guess that varies too, each frame is different, I think that wouldn't be too big problem, I currently ran 25/9 gearing with CS brakes and it was fine, If I choose that gearing it would be without back-brakes (or even mounts), even if it will hit the frame I can always build up my super hi-tech "tube+ ductape" chainstayguard..
But overall this gearing is OK? I mean, you can get some speed with this gearing too, would I be able to stay by side with street rider with 2.8 gearing if I really want to?