You shouldn't really get hung up on the idea that this is a beta of Windows 7. To all intents and purposes it is as close to final code as you'd need to get to benchmark. Take a look at paul thurrott's analysis of it to get a better understanding of just how far on Windows 7 is.
While I found the article really quite useful, it answered some questions I had. What I'd really love to know is just what the differences are when running games, surfing and doing the kinds of things you'd really be doing on a Netbook. Photoshop is really a meaningless benchmark for a Netbook, while it may reveal something about multiple cores and a strained system, it isn't really reflecting how the vast majority of Netbook users will be using the system. How about streaming flash in HD on Youtube, these are the kinds of benchmarks that I'd like to see, even if they end up being subjective opinion from the reviewer.
I'm lucky enough to have Ubuntu, XP, Vista and Windows 7 all running on same hardware to get a sense of what they all perform like, but this is on beefy hardware. Understanding what it's like on 1gb and a very modest processor is valuable stuff for those looking for that ultra portable.
For me, it'd be a deal breaker if I couldn't stream Youtube and other higher res video on the web. But if I knew that with XP it just worked ok,but was a little glitchy under Windows 7, that would again be really valuable information about which OS I would want to put on a Netbook.
I guess the best approach would be for people who already have XP to just slap it on their own Netbooks, run their own benchmarks that are meaningful to them and compare to Windows 7 and Linux. Time consuming and a shame tomshardware can't do it for us