My original system that I first installed RF2 on was a 4 year old Core2Duo E8200 with 4GB RAM, nforce 680i chipset, GTX460 and Vista 32bit.
I got some hitching problems at times and with the graphics tweaked and turned down some, I could race rF2, though it wasn't perfect. Even with the settings turned down I got pauses and that was a deal breaker. Hard to play the game at all with that setup, though I could still struggle along.
Then I got a SSD, upgraded to 6GB DDR2 RAM and installed Vista 64 bit. The SSD made an obvious difference, but the upgrade to 6GB RAM did absolutely nothing. Vista 64 and 32 bit made no difference. The SSD is usable in future builds, the RAM and Vista 64 were free, so no harm, no foul.
Last week that mobo was giving me issues and the SSD was severely limited by the nForce 680i chipset. In fact the mobo gave up the ghost and the system became unstable and unusable, so my hand was forced and I had to upgrade- I went to a Z68 chipset, i5 2500K and 6GB DDR3 with the same video card.
That made an incredible difference (in limited testing). Frame rates are smooth and I have every setting on max (but I can't turn on HDR or the road turns into a disco dance floor) and it is VERY driveable. That was a worthy upgrade.
So I don't know if this will help anyone else, but this upgrade went by a unique path so I thought it'd be good to relate to anyone looking to upgrade.