BTW, just for giggles I took one of my MII 10k boards and loaded up SD on it.
The system is a 1GHz CPU, 1GB RAM, 256MB ATI RADEON 9000 PCI and a 5400 RPM 2.5" drive.
With SD set to 30fps running in the windowed development environment, running a NAV playback in 2D mode, playing a song with spectrum analyzer display on, (and no other apps. running) has the CPU pegged at 99.889% avg. utilization with 480MB of memory in use. The avg. disk queue is neglible to light.
The bottleneck is clearly the CPU in this case. Granted this is running in the development environment which is probably not optimized for realtime use but it's pretty telling.
Adding another 200 MHz to the CPU wouldn't correct this and if I pulled the video card and ran with the VIA on-board IGP, I could probably topple the system quite easily running NAV, audio playback and performing library/playback searches/filtering simultaneously.