The Arctic Silencer barely exhausts any heat from the case, put your finger by the grille on the back and you have just the slightest breeze coming out, barely detectable. The amount of air that the AS is pushing out is so small compared to even a quiet case fan you really shouldn't worry about it. Looking at the new cooler, I'd be absolutely shocked if the AS was even as good as the stock cooler.
56C under load is incredibly low for an overclocked high end gpu on air are you really sure that is as high as it gets? Not what it says when you alt-tab out of the game real quick to check the temps, but what a program like riva tuner will record during actual gameplay? Temps drop 5-10 C in the few seconds alt-tabbing takes. Also the GPU will not get to its load temperature unless you totally eliminate any CPU bottleneck, but with a system like yours I'd assume you are playing in very high resolutions with all the AA and AF you can turn on.
Finally, 76 is not really that hot for a high end gpu. A 6800GT can easily hit 80 C, and a pair of ultras in SLI will sit around 90 with stock cooling. Granted the new cooler is far better than the ones on the 6 series.