The PPD difference comes from the huge differences in the dependency on the cpu between the two. If you had a liquid-nitrogen-cooled 8Ghz cpu, you could likely match/exceed the nvidia cards' PPD's with a 4870 on the smaller WU's. As the ati cores become less and less cpu-bound through mhouston's work, you'll see that the new WU's being issued for Nvidia will produce smaller and smaller PPD relative to the science being done since the benchmark machine will be doing more ns/day of simulation when the initial PPD mark is set with the more efficient core available at the time. At the end of the day, I believe we'll wind up seeing the PPD numbers matching what our expectations would be given the raw TFLOPS available and the observed efficiency rates of shader use. The Nvidia crowd should soak in the points while they can, because once the larger proteins start being crunched by them, their PPD will likely decrease drastically from what they are accustomed to now just by the fact that the ati client has become more efficient and is the benchmark reference by which everything else is compared to.