Pixel filling power
Theoretical peak fill rates and memory bandwidth don't always dictate real world performance, but they should give us an idea of where each card sits relative to its competitors.

  Core clock (MHz) Pixel pipelines Peak fill rate (Mpixels/s)Texture units per pixel pipeline Peak fill rate (Mtexels/s) Memory clock (MHz) Memory bus width (bits) Peak memory bandwidth (GB/s)
GeForce 6800 3251239001390070025622.4
GeForce 6600 GT AGP5008*20001400090012814.4
GeForce 6600 GT5008*200014000100012816.0
Sapphire Radeon X8003921247041470470025622.4
Radeon X8004001248001480070025622.4
GeForce 6800 GT35016560015600100025632.0
Radeon X800 Pro4751257001570090025628.8
Radeon X800 XL 256MB 400 166400 16400 980 25631.4
Radeon X800 XL 512MB4001664001640098025631.4
GeForce 6800 Ultra42516680016800110025635.2
Radeon X800 XT50016800018000100025632.0
All-in-Wonder X800 XT 500 168000 18000 1000 25632.0
Radeon X800 XT Platinum Edition52016832018320112025635.8
Radeon X850 XT52016832018320112025635.8
Radeon X850 XT Platinum Edition 540 168640 18640 1180 25637.8

ATI easily wins the peak theoretical fill rate war. The X800 XT and X850 XT Platinum Edition both offer higher fill rates than the GeForce 6800 Ultra, and the Radeon X800 XL boasts higher peak theoretical fill rates than the GeForce 6800 GT. However, the Radeons don't fare quite so well when we turn our attention to memory bandwidth. Although the Radeon X850 XT Platinum Edition boasts the highest peak theoretical memory bandwidth of the bunch, the All-in-Wonder X800 XT and Radeon X800 XL have less memory bandwidth than the GeForce 6800 Ultra and GT, respectively.

Of course, those are only theoretical peaks. 3DMark05 lets us test fill rates, albeit with synthetic tests.

Despite having a theoretical pixel fill rate advantage over the GeForce 6800 cards, the Radeons can't match their performance in 3DMark05's single-texturing fill rate test. It's been argued that 3DMark05's single-texturing fill rate test is memory bandwidth-limited, but with the GeForce 6800 Ultra taking top honors ahead of the Radeon X850 XT Platinum Edition, which boasts more memory bandwidth, that may not be the case.

Moving to multi-texturing, the Radeons begin to flex their muscles. Here, the X800 XL has a sizable lead over the GeForce 6800 GT. Heck, the XL almost manages to catch the GeForce 6800 Ultra, whose multi-texturing fill rate trails that of the Radeon X800 XT and X850 XT PE by a significant margin.

In addition to synthetic fill rate tests, 3DMark05 also includes a set of pixel and vertex shader tests.

The Radeons look comparably weak in 3DMark05's pixel shader test, but bounce back with strong performances in both vertex shader tests.