I couldn't agree more. I've done the same thing with things like AF and Trilinear. I'm able to do that with the NVidia card and only see a minor impact in visual quality. WHen I was running the ATI card, Nothing seemed to work except starting fresh. I sat here for hours changing each setting one at a time to get the best results and a usable frame rate. I was running an ATI HD 3450. I picket up an NVidia 9600 GT from a friend for 15 bucks. The 9600 is only a bit higher than the 3450 but in IL-2, I now bottom out at 18 - 19 fps instead of 2.
With the ATI card, I found it best to start from scratch. Use IL-2 to set everything and go into the control panel and set everything to either off or Application controled. Then I fiddled with each setting one at a time.
One thing I forgot to mention is that I use the forceware modified drivers from guru3d.com. I can't say enough about the improvement in both fps and quality. I installed those and my frame rate went up considerably on some maps and with making no changes in IL-2, and so did the visual quality.
I'll be in the market for a GTX 460 soon. I'm very curiouse to see if the improvement will be substantial on a low end system like mine.