I'm not sure what you need a faster CPU for with traffic shaping. QoS is not particularly demanding unless you are trying to push much more than usual cable-modem/DSL traffic through it. I have a WRTSL54GS for a WISP remote location acting as wired router for about 10 customers running QoS, ChilliSpot, and OpenVPN client (only for some admin traffic) and according to top never get anywhere near using the CPU to capacity.
My home config is WRT54GS v1.0 as purely wired router. I turned off WiFi, and have a WRT610n hanging off one of the LAN ports to act as an Access Point with router functions disabled/ignored. I have given up on "do everything in one box" because manufacturers never get all parts of that right, and they play so secretive with their WiFi code that it's hard to get it done right in OpenWRT. I have yet to see vendor router software that wasn't buggy as hell at plain old routing, not to mention lack of flexibility to add things like OpenVPN. OpenWRT works FANTASTIC as wired router so I have it do ONLY that job.