Neither MacBook Pro nor my Core2Duo server transcode from MPEG2 to h.264 at a respectable rate, so I'm considering building a dedicated machine to do that and any other computation-heavy work I may need in the future.

Here's the catch. I'd like to do it "on the cheap"

None of the open source software seems to take advantage of things like OpenCL, so I won't be needing significant graphics power to help the process. This will all come down to two things, IMO, CPU (cores and speed) and memory.

Does anyone currently have a system deployed for a similar purpose?