Dear Parky,
I have OFF installed on my PC. I play OFF and the occasional ROF.
These were the steps I followed during the upgrade of my PC for play OFF since Nov 2009.
New motherboard
CPU
RAM
1 x Ati 5970
2 x extra samsung monitors for eyefinity
But for me OFF still needed some tweaking so,
2 x WD Raptors (sorry but that was not the answer - returned it)
Then I received 2 kingston SSD (these SSD did not support TRIM in Win7 meaning Stutter problems) and returned them.
Got 2 x intel SSD (wow) no loading stutters while playing OFF. Now this is better.
Got a thermaltake 1200 power supply to run 2 x 5970 cards
Got an extra Asus 5970 (now I have crossfireX) even better FPS still without stutters
This is the logic reason I'm saying that SSD made the biggest difference in my setup playing OFF - like you said this is a OFF Forum.
Hope the info helps.
M