Pixel filling power
Higher theoretical fill rate and memory bandwidth numbers don't always guarantee better performance in real world applications, but they're a good place to start. Here's how the GeForce 6600 GT's theoretical peaks stack up.

Although the GeForce 6600 GT's unconventional rendering pipeline yields a comparably low single-texturing fill rate, the card's multi-texturing fill rate is monstrous. The GeForce 6600 GT AGP has a huge multi-texturing fill rate advantage over the Radeon 9800 Pro, which will be its most direct competitor as far as AGP cards are concerned. ATI has no plans to move the X700 series to AGP.

The GeForce 6600 GT AGP's impressive multi-texturing fill rate flirts with those of higher-end cards like the GeForce 6800, but its 128-bit memory bus brings it back down to mid-range territory when we look at peak memory bandwidth. Thanks to lower memory clock speeds, the GeForce 6600 GT AGP has 1.6GB/sec less memory bandwidth than its PCI-E counterpart.

Since theoretical peaks don't always determine real-world performance, let's see how the 6600 GT AGP's fill rates look in some synthetic tests.

True to their theoretical peaks, the GeForce 6600 GTs lead the way when it comes to multi-texturing fill rate. 3DMark05's single-texturing fill rate test looks like it might be memory bandwidth limited, at least with the 6600 GT AGP, which is clearly slower than its PCI-E counterpart.

Shader power
3DMark05 also has a trio of handy shader performance tests. The results of these tests don't necessarily predict real-world gaming performance, but they may help us to explain any performance differences we see later. Like some games, 3DMark05's shader tests have optimized code paths for shader models 2.0, 2.0b, and 3.0. I tested each card with its highest supported shader model: 3.0 for the 6800 and 6600 GTs, 2.0b for the X700s, and 2.0 for the 9800 Pro.

The 6600 GT AGP's performance in the pixel shader test is quite strong, but the vertex shader tests yield less impressive results. The Radeons clearly have vertex shader power superior to the GeForce 6600 GT. Somewhat surprisingly, the Radeon X700 cards beat out the GeForce 6800, as well.

Although the vertex shader units from ATI and NVIDIA aren't entirely comparable in terms of performance, these results show the architectural differences between the Radeon X700 and GeForce 6600 GPUs. The 6600 has three of NVIDIA's vertex units, while the Radeon X700 has six of ATI's. Also, the higher-end GeForce 6800 cards have six vertex shader units, but the vanilla 6800 has only five, which explains its relatively unimpressive performance here, too.