A desktop running Windows 8 Consumer Preview started up faster and generally ran faster than the same desktop running Windows 7.

Our test system running Windows 8 Consumer Preview started up faster, ran through our WorldBench 7 benchmark faster, and showed superior performance when browsing the Web, compared with the same system running Windows 7. In only one major test, our office productivity measure, did Windows 8 lag behind Windows 7 performance.
Obviously, these results are far from definitive, since they’re based on a preview rather than on the final version of the new operating system. But once Windows 8 is finally released, it is entirely possible that the performance will improve, since we had to use drivers that weren’t yet tweaked for Windows 8.
The results also jibe with what readers who had installed the Consumer Preview told us in a recent survey. About 40 percent of respondents said their machines seemed faster with Windows 8, and only 9.4 percent said they seemed slower; nearly 45 percent noticed no significant change.