The Hyper6 will just about outperform the xp-90c if you fit it with 2 80mm fans, however this will be a lot noisier than the xp-90c with a single 92mm fan.
Personally i'd go with the xp-90c. I've owned a hyper6 with 2x 80mm tornado's fitted, and it made my eardrums bleed.
Apparently, a lapped TT BT can beat both of those with stock fan, especially if you know the trick of stuffing the empty space with something like foam so the air from the fan doesn't escape through