I've found gaming performance to be excellent on the Release Preview, so I imagine the final version will only improve on that. However, I came across some compatibility issues with certain games (LA Noire, Crysis 2) and that is simply unacceptable to me. I blame the games developers, as the vast majority of games run without issue.
As drivers mature I have no doubt that Windows 8 will be the faster operating system, just as Windows 7 improved over Vista and Vista improved over XP (yes, benchmarks confirmed it was faster in most games despite people's perceptions).
@patseguin - SLI is always disabled by default and with driver updates, which to me seems counter-intuitive.
Considering that the issues with Crysis 2 and Windows 8 are entirely in DX11 (with DX9, which is the default, 8RP smoked 7 rather badly), I'd wager that it has to do with one of two issues; either Crytek had an OS-ism in the DX11 code (which is utterly inexcusable) or there is an issue with the runtimes (specifically, those for DX 11). I'm thinking that the former (not the latter) is the issue (as other games that support both DX9 and DX11 don't have the issues Crysis 2 does).