Something is sucking the life (FPS) out of FSX

One more possibility, I think Word Not Allowed mentioned this recently - watch your HDD free space. I'm running FSX on a dedicated SSD and recently was down to 10G free space out of 256 total. I noticed FPS were increasingly lower. I deleted about 40G in scenery purchases, and - maybe it is a placebo - but I seem to have gained 5+ FPS in tough scenery like Imaginesim KLGA. I seem to recall a recommendation to keep about 20% of your HDD space free - seems to have worked for me