I recently formatted my HD. Since then I have noticed that my FPS drops considerably if I'm close to any AI traffic ???. This bothers me the most when I'm approaching and other aircraft become visible. I have tried by setting Aircraft settings in the Display section to minimum and that doesen't help. It also won't help if I set my fraffic density lower since I only need one or two planes to have my FPS drop.
Before I formated I coppied my aircraft folder to another drive and then back again after re-installation to lower my "workload", but I don't see how that could have effected!