Could be a VRAM issue if you are using max textures, (high resolution 1080p+) and/or high levels of AA. Monitor it with MSI Afternburner or similar.
If that doesn't seem to be the problem, turn off motion blur, SSAO, and reduce shadow quality. I played on a comprable system (overclocked i5-750, GTX470) and had 90+ fps.
If that doesn't seem to be the problem, turn off motion blur, SSAO, and reduce shadow quality. I played on a comprable system (overclocked i5-750, GTX470) and had 90+ fps.