The only DX10 game that is coming out this year (to my knowledge, tell if there is others) is Crysis, and even at an interview they said all the footage and screenies you have seen were all runing on single core CPUs and DirectX9 hardware (well some newer ones may have DX10 effects but even still, the ones in 9 look tasty). UT07 was designed around the 6800 and 7800 series of cards, so if you have a 7900 or X1900 card you should be fine (and Unreal Engine is DX9).
And if your wondering why the 7950 cards are only clocked at 500 each was because to get two G71 cores clocked at 650 it would require two 6-pin PCIe plugs for one of those cards(because it uses more power), meaning if you want to have two of them for quad SLI, you would need 4 6-pin PCIe plugs (pretty much all PSUs that have PCIe plugs only have 2). You could use molex to PCIe adapters but that will eat up a lot of plugs and you would need a HUGE amount of power. So SLI 7900 GTXs will eat one of these cards up.