Uhm... ATi's naming of the cards is currently as clear as it could be, higher the number higher the performance, which is what people usually expect. They also have the cards clearly categorized to amount of thousands (5800 = high end, 5700 mid-series and so on).
I don't know how much you've been following the GPU naming problems with nVIDIA, but there has been a lot of cards renamed with exactly same product (even whole series of cards, just in January 2010) and the same G92-GPU core has been used with different clocks for many cards with very minimal amount of difference them. Choosing which card to buy might get a bit hard to those who just watch the numbers, not to speak about the GT/GTS/GTX/Ultra-thing they had a few years ago.
Even those who think they know something about the business should do the research of reading the reviews from as many sources as possible in order to get the realistic picture of what you're buying, and if there's anything better in the same price range.
