more specific, is your pc use heavy cpu weighted or more data handling for which I would rather recommend a fast raid hdd setup with SCSI drives & 15000 rpm. Maybe you just try some sort of system testing programm to really determine where the bottleneck in your sys is. I have also been on the way to simply more cpu power, but thorough testing before has saved me a lot of $. If you have really CPU problems then the Intel P4 with HT should bring a bit of improvement, they can intelligently multithread app internally.
best to you,
cosmic