What's faster? I've never read even the most fervent proponent advocate it as either a more efficient or speedy (from a usability) perspective. That isn't to harsh on it -- the compromise is better touch usability and purportedly better aesthetics, although that is deeply subjective.
From a usability perspective, the start screen is faster than clicking items on the start menu. MS wrote a very convincing blog post on the matter full of statistics (which i agree with mostly).
Similarly, the ribbon interface in explorer allows for quicker access.
It also has lower requirements than windows 7 IIRC, so that indicates it should be snappier, and it has faster boot times.
From a usability perspective, the start screen is faster than clicking items on the start menu.
However, that's only true because Microsoft kneecapped the Start menu in Windows 7.
I wouldn't use Windows 7 without Classic Shell (http://classicshell.sourceforge.net/) and I'm sure the same will be true for Windows 8, if/when I'm forced to move to it.
