Nope, I tried without any updates (always keep Windows Update off). Then decided to give SP1 a try just about 2 weeks back, was without SP1 before then, still the same problems. Yup, HDDs set to never sleep (the PC as well)
Yes, BIOS is updated. But would an outdated BIOS really cause stuttering and hangups all of a sudden?
Got a spare hard drive sitting around? If so, disconnect old HD, connect temporary HD, boot w/Win7 DVD- delete any existing partitions- create new partition(s) quick format, install Win7. Test your performance from there.... Sometimes Windows just breaks- re-partition/new install quickly fixes most problems without causing loss of hair to owner PS- you mentioned your CPU is 73c while gaming, what's it's temp during normal desktop (web browsing etc..) use? Maybe your heatsink fins are clogged and automatic temperature throttling is kicking in?