This article posted to C|Net got me to thinking. In the article, they talk about vaguely defined "benchmarks" showing that Windows XP with the beta of Service Pack 3 outperformed Windows Vista with Service Pack 1.
I can only say one thing: duh. Quite frankly, I would have been more surprised if Vista had outperformed XP.
This really is an apples and oranges comparison because Vista is a newer and more complex operating system. And I'm not exactly a Microsoft fanboy, either - I'm typing this on a Mac, using a Java journal client. Of course it is going to run slower on the same equipment than an operating system that was released six years ago. I'm sure Windows 98SE will beat the pants off of XP on the same equipment, too. Leopard, released a few months ago, won't even run on hardware circa when OS X first came out and will almost certainly run slower on machines that were top of the line when Tiger was released. Hey, while we're at it, we could compare Doom to UT3 to see which runs faster!
If they wanted to do a more fair comparison, they would have compared them on different machines - top of the line machines when their respective operating systems were released, using adjusted benchmarks. Being that machines are much faster now than they were in 2001, I wager that the difference between them would be a lot less.