Recently, I have noticed my frame rate take a hit. It varies from plane to plane and where I happen to be (Chicago O'Hare practically made my computer choke). I have heard that reducing the # of planes you don't fly can help with the frame rates. I also use the Global Terrain Mesh (70M) cached as well as the addon scenery cached (could un-cacheing them help)
I also use FSAutostart to shut down background processes and I have the NoCD.exe for FS9 (I do have the CDs and purchased the product from a Best Buy here).
Any suggestions?