Not true at all. 3DMark2001 is still the best overall system test that simulates real usage. While most NEW games take advantage of DX9 functionality, many do not. And even the ones that do will run very well on a DX8.1 card as well. Most games require DX8.1 or better while only a handful actually require DX9.
Yes it is true that 3DMark05 is a better test for DX9 games, but that's not all you do with your computer is it? Also, neither 2k3 nor 2k5 are affected much by CPU power. 2k1 is greatly affected by both CPU and GPU, so it is much more valid as a general systems test.
Yes it is also true that there is a bigger difference between the X800XL and X850 XT PE in DX9 games, but nowhere near double. The price however is just about double in most parts of the world.
X850 XT is slower than X850 XT PE (which is what I compared).