ZDNet have some performance benchmarks which pit three different spec machines against each other using Windows 7, Vista and XP. The results include information on bootup times, cache usage and application performance testing. Although this isn't an in depth test, it does give a good indication of the performance you can expect from Windows 7:
http://blogs.zdnet.com/BTL/?p=22006
The article is available to read here:Windows 7 performs better than Vista and is also faster than XP, although XP remains more capable for devices with limited memory and outdated graphics.
Subjectively, the change from Vista to Windows 7 is like releasing a car’s handbrake. This significant increase in performance has several causes: faster system startup and shutdown compared to XP and Vista; improved parallel processing; and faster loading of drivers and operating system components. Enterprise users will also appreciate the faster login to a domain.
Microsoft has also thoroughly revised the SuperFetch feature, which results in quicker operational readiness after startup. Anyone migrating from Vista will notice a reduction in disk activity after startup, because SuperFetch spends less time loading applications into memory in Windows 7, which means less waiting for the system to be ready to use after launch.
http://blogs.zdnet.com/BTL/?p=22006