Overclock.

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Going from 27 to 33 FPS is not an increase of 20%. Your playing on the same settings and only getting 6 FPS more. Going from playing on medium + no AA at 27 FPS to very high + 2x AA at 27 FPS could be considered a 20%, but not just 6 FPS at the same setting . That's like saying going from a 8800GT to a 9800GT is a 20% increase in performance.

The thing is that maybe you get 33 FPS most of the time, but it will drop sometimes and usually it will be during combat scenes where it matters so imo, 33 FPS is too low to be playing at.

33 fps is an average sometimes it dips down to 30 but never less and is perfect for crysis, it has motion blur which makes game look perfectly fine even in intense action  . Btw 8800gt and 9800gt is exactly same thing but 9800gt eats less power i think check any hardware forums

btw going from 27 to 33 is exactly 20% increase in same settings (was very high no AA) 27 divided by 100 times 120 = 32.4 

now if i had higher fps for ex 60 than i would have an increase up to 12fps increase if overclocked the higher the fps you're getting before overclock the more of an increase you will get.