Overall, this was a good article. I've seen driver updates on past hardware that netted more significant FPS improvements than is show here, but the time frame for optimizations is consistent with the article introduction. Also consistent with the article is the fact that the larger improvements don't usually occur on the high end cards.
Disclaimer: This is not a fault in the article, just speculation on one of the results.
Referring to the Crysis Very High setting on the Radeon 4870:
In the Very High setting, fluctuations of the frame rates can also be seen. There does not appear to be any reason for these variations, although a performance increase is almost always seen.
It appears 1280x1024 is cpu limited, as you see a fair FPS improvement at this resolution (and not others) when overclocking.
Moving to 1680x1050, you see more significant improvements as the burden has shifted back towards the GPU, allowing the enhancements to be seen.
At 1920x1200, we are simply reaching the limits of the hardware, so the enhancements are less relevant.
It seems one of the enhancements affect AA performance in Crysis as it seems to be improved across the board. I'll leave you to figure out the rest, as I'm short on time, but I'd wager the enhancements involve trading more efficient processing of data on the video card for more driver overhead. This would explain why more CPU limit settings are seeing lower rates, while more GPU intense settings are seeing benefits. The only real oddball is 1680x1050 at high, but I'll bet with a little time, it could be explained as well.
On another note: Did the Catalyst 8.8 improve performance over Catalyst 8.6 in CF mode when both were overclocked. I suspect the answer is no, but it seems there may be more CPU overhead in the newer drivers. Given more CPU cycles, an insignificant, but measurable improvement may be measured. (My interest in this is purely academic as I don't own a newer ATI card at the moment)
That said, I'd be interested in a similar article with mid/high end video cards and a mid/high end processor. What kind of real performance improvement (or lack there of) can someone with a GeForce 8800GT or Radeon 4850 expect with paired with an Athlon X2 6400+ or a Core 2 Quad Q6600 (without overclocking).