I've actually found that the old 3dmark2001SE is a good estimate of AH performance. In general, the PREVIOUS generation of 3dmark benchies always give more consistent real-world performance results than the latest version. Give 3dmark2001 and 2003 a try, and I think you'll see that sort of perf increase with the new card.
The last 2 3dmark versions, 2005 and 2006, seem pretty much worthless to me. A 7800 will crush my 6800GT in 3dmark2006 even with the same cpu, but in AH a 7800 will probably show less than a 10% framerate increase over my 6800 because AH is somewhat cpu limited.
The intangible thing you get with the newer vid cards, especially with AH, is that you can turn the resolution and antialiasing waaaay up, even if you can't move the in-game sliders any more. That's why 3dmark2001 and 2003 are still decent performance indicators for AH... Their scores aren't inflated by card features that AH doesn't use.
Remember, AH still runs on GF2 era hardware, so just about the only things that increase AH fps are pure fill rate and cpu power. The newer vid card features only get you eye candy like antialiasing and that's why buying a brand new but lower-end video card can give disappointing results in AH. Because the low-end cards really don't see much of a pure fill rate or "pixel pushing powr!" increase even if they support the latest accelerated standards.