You don't really need people to buy new hw - there will be enough gamers with similar CPU (Core 2, and if you're really a benchmark freak you can also ask people to downclock their processor), deactivate some RAM so everybody has 2Go (but realistically there's no need, games don't show differences over 2Go).
I think the only difficulty is agreeing on standard resolutions, a set of tests and the games/gx bench.
- 1024x600 (so netbooks can do it)
- 1440x900 (most gamers)
- 1920x1200 (Full HD monitors, close to 1920x1080 for those playing on TV)
And maybe 25XXxXXXX for those with a big monitor.
Everybody could run the first two test, a relevant number could run the third. Just eliminate those that have a Core2 < 2Ghz or less than 2Go of RAM, and the rest just don't overclock or downclock.