This game definitely runs much better on a faster rig. I upgraded from a dual core Opteron 185 overclocked to 2.8 GHz and with 3 GB RAM and an 8800 GT to this rig. I think I got a nice deal for $600, essentially brand new.
Core i5-3570K (quad core, Ivy Bridge, unlocked, OC to 4.2 GHz, can easily do 4.5 GHz)
Corsair H60 Water Cooler HSF
8 GB generic RAM from a Dell (2x2x2x2)
ASUS P8Z68-V LX mobo
EVGA GeForce GTX 560 2GB DDR5 (special model for Best Buy)
128 GB Kingston HyperX SSD
Windows 8 Pro
Antec BP550 Plus modular power supply
Antec 300 case (only has the rear and top fans)
DVD-RW drive