I've got a 433 running 90-100% cpu most of the time. It's pushing about 20mbps of Internet traffic. It's got a couple mange/queuetree items to prioritize VOIP, and that's about it. It's got 1 wireless nstreme interface, and utilizes one of the ethernet interfaces for 2 vlans. Would I see any more speed potential by upgrading this to a faster RB?

I did setup a mangle to identify http traffic and a queuetree to limit that to 10mbps and that did not improve performance through the RB for non http uses, even though http traffic did decrease and total traffic was closer to 10mbps then. So it's apparently a connections/pps caused slowdown more than a megabit slowdown I'd guess.

how much pps you have?

you could check routerboard.com for tested pps of device