case is eating too much of the budget imo.
go for a cheaper one and then pick up either an unlockable 2GB 6950 or a 6970 as lordjummy said.
no point in wimping out on the gpu on a hardcore gaming machine simply for a prettier case. Cases can easily be modded for much much less money.
also I'd recomend a 2x2GB memory kit at 1866 or higher long before a 1333 2x4GB kit. try to get 1600 at least lest youre memory will be a major point of lag. Actually the 2x4GB 1866 kits are just 80$ anyways.
also most people on SB have run into an issue with 4GB sticks and overclocking. Paulieg and a few others would be able to tell you more.