Nice review, SLI in VISTA vs XP

http://www.hothardware.com/article [...] P1/?page=2

Our quick-take look at NVIDIA SLI performance in Windows Vista and DX10 versus DX9 in some gaming scenarios, paints a pretty detailed picture. The basic moral of the story at this point is that, as expected, NVIDIA has been able to make significant strides in terms of increasing performance for multi-GPU rendering with Microsoft's new operating system. Though Bioshock was the most significant example of recent gains and driver optimizations with both Vista and DX10, SLI performance in Vista is now roughly on par with Windows XP performance with like settings, with a 5 - 15% swing in favor of NVIDIA's more mature XP drivers, depending on the game engine involved. Regardless, gone are the days it seems, of sub-par NVIDIA SLI performance in Windows Vista. We look forward to bringing you more insight with respect to the state of DX9 and DX10 gaming on both NVIDIA and AMD platforms in the next week, so stay tuned.

it can be forced