Windows XP is fast.... when you first install it. After a year of use, windows xp becomes bloated and slow whereas windows vista / 7 is still running the same speed.
Windows XP offers little to absolutely no protection to the end user from most of the more sophisticated viruses out there. With windows vista / 7 you don't even need a virus scanner if you are vigilant about what you authorize (User Access Control). I feel so much more secure on Vista than I ever did on XP, it's also 1000x more convenient. Drag/drop, copy/paste, whatever is a lot more streamlined with prompts that actually let you skip files instead of failing outright.
Yah Vista had/has its problems, but the past two years that I have been using it on both my desktop and laptop I am absolutely confident I would NEVER go back to XP even for a modest gain in speed.
EDIT:
The benchmarks that are in that article all show one thing. XP IS SLOWER THEN VISTA AND WIN7. Why? Take the boot time for example. Vista and Win7 load up all their graphics and everything else associated with the OS in only 1 second longer than XP. Take the iTunes encoding, that has nothing to do with OS performance and everything to do with Processor and internals. The Shutdown performance is a quasi-worthless statistic, but revealing anyway. It is a tough sell for XP, it is doing so much LESS than the others, yet takes the same amount of time to do it. That sounds like a LACK of performance to me. Installing anything on that XP machine that starts on boot and I guarantee that startup time will grow exponentially whereas Vista/7 will still be around 40 seconds.