Since I had to uninstall my ATI drivers anyway, I figured I run a test:
There's most definately something not right with the Radeon 9500 and up cards in AH2. My GeForce 4 Ti 4200 (put it back in for a test - 41.09 drivers) delivers over 2x the framerate of my Radeon 9800 (standard 128 MB, NOT SE or Pro/XT) in 1.997 at 1280x1024 32bpp (no FSAA or Aniso).
The new Cat 3.10s do not seem to be any better than the 3.7s for AH2. I haven't yet tried them in anything other than AH2, so I don't know if OpenGl is still broken, as I found with the 3.9s.
A couple things I've noticed, between the nVidia and Radeon cards, in AH2 1.997 is that on the Radeon cards there is a very noticible stutter that occurs at a very regular interval (offline at least) of about 1 second. This started with 1.995 for me.
1.995 and up are nearly unplayable with all the detail sliders in AH2 to the max (25 fps on the runway, dropping as low as 17 fps in flight - 1280x1024 32bpp). At about 80% the framerate is acceptable at about 39 - 45 fps. The triangle count drops from well over 20000 to about 12000. Strangely enough, turning on 4x FSAA has no significant impact on framerate, 2x has none at all. (On the GeForce 4 TI 4200 you couldn't turn on 4x FSAA and get even 25 fps in AH 2, and there was a very large performance hit enabling it.) This would lead me to assume that this isn't a memory bandwidth/fillrate issue with the Radeon card, but rather something else. It might be a driver issue, or it might be something to do with AH2, it's really impossible to tell for sure. Considering that in every other game I have the Radeon 9800 is significantly faster than the GeForce 4 Ti 4200 I think it might be something to do with AH2. AH1 runs at my monitor's refresh rate (85Hz - 85 fps) with 4x FSAA turned on at 1280x1024 32bpp under nearly all circumstances. The first beta version ran MUCH faster on the Radeon card and performance has been dropping slightly in future releases. (I got 75 - 85 fps down low with 4x FSAA on in 1.9901 for example.) 1.995 was the big hit though.
I sure hope HT can track this one down.
Detailed hardware specs:
Athlon XP 2400+ @ 2.13 GHz (2600+ effectively)
Asus A7N266-C bios 1.05 b2, newest nVidia chipset drivers
Radeon 9800 128MB standard, cat 3.10 (was using 3.7 previously)
4x AGP rate, Fastwrites enabled (made no real difference either way)
Direct X 9.0b
512 MB DDR
120 GB WD SE HDD
nVidia Soundstorm audio (ob)
Windows 2000 SP4 + all critical updates