Just an update. Been trying to figure out whether my CPU or my OCZ memory was causing errors / instability. I was just about to conclude that it was the CPU, but decided to run Memtest86+ (all tests) while I was at work. Set memory to rated speed and timings (DDR466, 2.5-3-3-7, PAT disabled). Came home to pages of errors. I had not been running Memtest for much more than an hour before now - wasn't long enough. So I'll call OCZ support for more answers on that. Put my Mushkins back in, FSB 240, 5:4, PAT / Turbo enabled - Prime95 and FAH together (100% load) for 24+ hrs and no errors. Now I'm back to seeing how far I can push the Mushkins at 1:1 for now. I wanted to avoid RMAing the OCZ if possible, but I'll see what their support says.
Thanks to all who have been helping me with this. Still open to suggestions.