I have the same problem ,but not in ISI games .
Rfactor and Arca run smooth for hours, but last night i had complete freeze four times in Race 07. Only happens in Race 07 for me.
4GB OCZ platinium - 8800 GTX 768mb- 1000GB HDD samsung spinpoint-
Gigabyte P35-DQ6 mainboard - Dualcore E6850 and Cooler master5 case.
Should run smooooooth !!!!
( well if it runs its great)