FS9 sliders and Big Airports

I've been reading all of the tips and trix in these forums for a few weeks. As a whole, I'm very happy with FS9 performance on my system. I've got a P4 2.26/533mhz 768MB PC2100 RAM, GeForce4 ti4600 128mb (also used a ti4200 64mb - that upgrade helped tremendously). I've got the FPS locked on 18 with all the sliders to the right except water effects - just don't like it, shut it off. I run the sim a 1024x768x32 w/2xAA and 2xAF. I can maintain 18 FPS in every situation/weather conditions except at major airports. KEWR = 12 fps, KJFK = 10 FPS, KCGX = 10 FPS, KORD = 9 FPS, KLAS = 10 FPS ...you get the idea. So I've done a fair bit of tweaking with the sliders, and I can't get more that 2-3 more FPS at these airports changing anything. If I turn off AI, shadows, reflections, autogen, scenery complexity, etc. I still only get about 15 FPS. My question is what is the frame rate hog at the big airports? Any ideas?As soon as I get some elevation or distance from the airports, frames skyrocket. I could easily lock FPS at 25 outside of the major metropolitan areas, and I can't find any way to get better frames by adjusting the sliders...Suggestions welcome!Thanks,sg