Hexus.net take a look at NVIDIA GeForce 7800 GTX 512:
NVIDIA's efforts with the new G70 earn them the overall performance crown back, and by quite some margin. At 550MHz across the board and with 512MiB of memory running at 1.7GHz effective, it would have been embarassing had that not been the case. That didn't happen, though, and the reference-clocked GTX 512 has no trouble dispatching GeForce 7800 GTX and Radeon X1800 XT to the sidelines.

Quite simply a performance monster, and one that'll take ATI a big effort to beat. The GeForce 7800 GTX 512 impresses hugely, from quiet and efficient cooler, to manageable increase in power draw over the original GTX, with monsterous performance and day-zero availability in-between.
Another review can be found on Bit-Tech:
F.E.A.R.: There were some huge differences in performance between the GeForce 7800 GTX 512MB and the chasing pack in F.E.A.R.. We saw a 29% average frame rate increase over XFX's Extreme Gamer Edition at the XFX's best-playable settings, which equated to a 32% average frame rate increase over the X1800XT. The minimum frame rate was where we were really impressed, though. We saw a 133% performance increase over XFX's Extreme Gamer and a 115% increase over the Radeon X1800XT. Even with 4xTSS AA, we experienced a higher minimum frame rate than what was experienced on the X1800XT 512MB and XFX 7800 GTX Extreme 256MB cards at 2xTSS AA!

Quake 4: We played Quake 4 at 1600x1200 0xAA 8xAF, which were the same settings that we found to be best-playable on the Radeon X1800XT 512MB when using Ultra Quality mode. We were more than surprised at the gaming performance at these settings. The average frame rate was a massive 58 frames per second, compared to the 43 fps that we experienced on the Radeon X1800XT. The minimum frame rate increased from 19 fps to 29 fps, which is another impressive frame rate increase. However, when we reviewed the Radeon X1800XT, we felt that 1600x1200 2xQA AA 4xAF High Quality looked better than 1600x1200 0xAA 8xAF Ultra Quality because we feel that the game needs at least 2xAA. We found that we were able to play Quake 4 at 1600x1200 2xTSS AA 8xAF Ultra Quality on the GeForce 7800 GTX 512MB. This was with smoother gameplay than we experienced on the XFX 7800 GTX Extreme Gamer at 1600x1200 2xTSS AA 4xAF High Quality.

Day of Defeat: Source: In Day of Defeat: Source, we found that we could not increase the quality settings above 4xTSS AA 16xAF with maximum in-game details, including full HDR, but we were able to use High Quality driver settings for free. Even with high quality driver settings, the gaming experience was smoother than we have seen on any other single GPU solution.
Other previews and reviews with benchmarks can be found at Tech Report, TechwareLabs, HardOCP, PC Perspective, AnandTech, Guru3D and Digit-Life.