Apparently, after a bit of overclocking, a lucky guy has gotten a gpu performance world record (for now) using an nVidia GeForce 7800 GTX. With a stock clock of 550/1700(850DDR), the GTX is already a beast of a card. That wasn't enough for these guys who have managed to get over 13,000 3dmarks using exotic cooling, bringing the card to an incredibly 810MHz GPU and nearly 2GHz memory (1000MHz DDR). They achieved close to 19,000 marks in 3dMark05. While this isn't exactly a comparison of what you can pick up off the street, it's impressive and demonstrates potential future capabilities of the current nVidia lineup.
Like most super exotic situations there isn't much word on stability or how long it could be kept up, but likely a simple water cooling solution for the GTX could bring someone near this level of performance. With stock video cards now occasionally being offered liquid cooled, and multi GPU being a new hot topic, performance is ramping up dramatically. Just in time, too, as the games being released, regardless of genre, have taken incredible steps and are more demanding than ever. There are photos of the card and the setup being used in the link.