You were set at 1024 before you installed the hi-res pack, but without it you're running at 512 (even if set at 1024) -- the 1024 textures aren't included with the base install, as far as I know. So you might have been running it, but really were doing 512.
For your video card I wouldn't even recommend 512! I'd stick with 256 or (gag!) 128. Looks worse but trust me it helps FPS and video lag issues.
make sure you optimize objects and terrains, you turn off skins (if you can bear to) and disable weapons effects, disable animated water, disable vehicle effects, and lower your resolution to 1024x768 (any lower and the game looks like crap).
Turn off any and all anti-aliasing in the card's control panel, and if you have an option set it to "performance" instead of "quality"
I had a huge FPS hit this last update (2.09). No reason for it. It just didn't install the patch properly, or who the heck knows. I ended up renaming my Aces High II folder to "Aces High 2" and re-installed AH with a freshly-downloaded full install (no patch), reinstalled hi-res, copied my files from "2" back to "II", then removed the surplus directory, and I think that's fixed it. Last night I was in MWA and didn't have the crappy FPS I'd had the past week or so. I'd suggest doing the same. It might help.