I have two BFG 8800GT OC's myself, purchased when BB had them on sale. Apart from the noise/heat I like them alot so far. Cryris is the only game I have played so far that challenges this system.
Still waiting for the Crysis patch that is supposed to improve SLI/Crossfire performance. But right now, at stock speeds with a Q6600, I see a 16% difference at 1680x1050 everything at high with 0xaa/0xaf. But if I enable fsaa & AF, the increase goes up to 46% (4x/16x) for the two in SLI. At 2xaa/16xaf there is a large difference at 21 fps vs 31 fps average, and although it's playable at these settings, I'd like a bit more performance still, hence I am eager for the patch. But compared to the 320MB 8800GTS I had, the pair of 8800GT's is a Crysis Dream.
edit: just saw your OS....You may want to look into the current Vista 64-bit SLI stability/compatibility.