I'd probably do it gradually, when I was ready for my next big upgrade. First would come the dual PCIe slot motherboard and a good A64 CPU to overclock, hopefully reducing CPU bound problems as much as possible. Add in a 6800 GT and I'd be set for a little while, until I felt the need for more power. At that time, grab another 6800 GT at a cheaper price, and I should be seeing a better and cheaper boost in gaming than if I were to upgrade from a GT to a 6800 UE fall refresh card (would likely be out for a while by the time I felt the need to upgrade). This is assuming all situations are permitting.