That's not true at all, DX10 was not only meant to improve graphics (which it does) but it was also for improving performance on the same hardware (which it does). Vista is not resource hungry, people who say that are ignorant; yes it will say it is using a lot of RAM but it's not actually using it (as in preventing apps from using it), it's caching it so applications can access it faster. It's called advanced memory management.
In any case, Windows 7 and DX11 are coming up in about a year so don't wait, either get a DX10.1 card now or get a DX11 card in the future.
Also, that magazine scan is awesome because that mid-range config is nearly identical to mine, I'm happy I can run it at my native resolution on fairly good settings.