I have "low end" specs compared to many others posting, so when the game is only using 30-50% of the resources available to it, the performance hit is even more noticeable. Allowing the game to utilize all the resources available would increase performance on my system massively.

OS: Windows 7 (x64)
CPU: Intel i7 930, 2.80GHz (8 CPU's)
GPU: NVIDIA GeForce GTX 470
RAM: 4GB