In my experience with AH2, to run out of memory on a 128MB card, you have to set resoultion to 1600 x 1200, AA to x6, AF to x16. But there is no compelling reason to bother with AF at that resolution, it's almost impossible to see any effect. So 128MB is enough to comfortably run AH2.
My A-I-W 9800 Pro runs AH2 well enough, monitor refresh rate (85Hz) most of the time in flight , at 1280 x 1024, AA x6, AF off, other settings to max quality. Low FPS is around 70. It runs AH1 @ monitor refresh rate 100% of the time and with v-sync off is in the 200+ range. Results are CPU dependent. The same card on an AMD Athlon 2000+ system may be as much as 30 FPS slower.
On the other hand, my Athlon 2500+ (running @ 200 x 10.5) with a 9600 pro (oc'd) turns out around 60 FPS.