ShaderMark 2.1, GL_EXT_reme, D3D Rightmark 1.0.5.0
ShaderMark
ShaderMark starts us off with simple confirmation of the power the R4-series of ATI hardware in full four-quad mode. Clocked at 540MHz, the X850 XT PE obviously has no trouble beating the 400MHz XL.
GL_EXT_reme
That fact manifests itself again in Humus's simple GL_EXT_reme OpenGL 1.x benchmark.
D3D Rightmark 1.0.5.0
Rightmark 1.0.5.0 rounds off the look at theoretical performance. X850 XT Platinum Edition, sitting as it does as ATI's most powerful SKU, is able to outrun the slower X800 XL. However, when you take into account price as well as performance, the X800 XL's performance looks even better. I'll come back to that with my closing thoughts.