5850 = very close to the speed of a GTX 295 or something
5870 = faster than a GTX 295
5870x2 = complete domination and possibly may be the fastest card on the market even when Nvidia GTX 300 cards come out only because Nvidia might not be able to make a dual chip GPU this time around
As for the case....yea i like the HAF series, the 932 definitly wouldn't fit on the table, i have mine under but the 922 should do good. They say the 922 has the best airflow if you add the side panel fans becuase the like front and top fans that come with it are the same size as the one in the HAF 932.