It seems that your CPU might just do it after all, but even though it's mainly your GPU involved here, have you tried running the game on Default graphic settings (especially without all AA stuff ? that you shouldn't really need with 2.5 IR) ?
[color=#009900]Windows 8 / Linux 3.9.3-pf Ubuntu 13.04 -- 64 bits
Intel Core i5 3570k OC @ 4.2 Ghz
Nvidia GTX 660Ti
2 x 8 GB Transcend Ram @ 1600 Mhz[/color]
[color=#009999]
[color=#0000ff]Whατ ις ηστ lσgιcαl ις ηστ ρσςςιblε.[/color][/color]
Intel Core i5 3570k OC @ 4.2 Ghz
Nvidia GTX 660Ti
2 x 8 GB Transcend Ram @ 1600 Mhz[/color]
[color=#009999]
[color=#0000ff]Whατ ις ηστ lσgιcαl ις ηστ ρσςςιblε.[/color][/color]