I have quite a high end rig but even with SU10 etc, still seeing weak FPS at large airports, such as KJFK default.
What needs to happen, but which I doubt is happening, properly at least, is that the selected LOD settings should only apply to a certain radius around the aircraft. Beyond that a lower LOD should be drawn.
When descending to about 2500 ft, the radius should start to reduce down and when on the ground only needs to be about a mile or so. This should make a huge improvement to FPS.