Scenery fps..

I am trying to track down an fps porblem that has been going on for a while now, below are my specs and you can see that I have a pretty decent system but tonight I was landing at katl on vatsim and i was getting a steady 10-9 fps with the pmdg 737, it is even worse with the feel there 737, the only time the fps is 25 or better is in a plane using the 2d cockpit. I have quite a few addon scenery's installed including south productions katl which shouldnt be very tougth on frames. I have a few ga airports, fly tampa kmia and kbos, and I have simflyers jfk las and mco and a basic kden addon which adds the new r/w. Does just having these airports installed cause a loss in fps even though I am not flying into them all at the same time? I also have ge pro and ultimate terrain usa. SO basically im asking does the number of addon scenerys you have alone effect fps?