I would say out of the case. Pushing inside will theoretically increase temps.
True and this is how I see it as well, but Corsair is saying because the fan is reversed, it will in turn suck in cool air from the outside rather than taking the heated air from other components within the case to cool your CPU.
I decided in the end to push air out while installing a second fan inside the case to push the air to the H50. I won't say this is the best cooler, but it does perform pretty much on par with the Xigamtech HD1230 back on my C2D E8400. A bit expensive for watercooling considering its performance imho.