PR rating is redundant.....PR is Peformance Rating, at least I think it is...lol. correct me if i'm wrong, cuz i have a habit of correcting people when they're right, heh.
And officially, its the speed at which a regular Athlon processor would have to be in order to perform the same. But, it just so happens that it is also very close to Intel's speeds. And some benches actually show the PR of some XPs to be lower than an Intel of equal performance...but those are benches, and you can't trust a lot of them (though as an AMD fan, its fun to say they're fact, lol).