Just playing with FSX today - trying to get a handle on frame rates and thought I share my findings.

FEX, GEX, UTX installed and Default 172 and PMDG J41 at JFK with 2560x1600x32 screen sitting on runway:

All settings as low as possible/off:

172: 200 to 400 fps
J41: 40 to 50 fps

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Maxed everything except Autogen Density @ none and no AI traffic. Weather maxed (no thermals), distance maxed. AA, Trilinear on.

172: 85 fps
J41: 35 fps (18-22 when flying)

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Same as above, but add thermal visualization:

172: 60 fps
Note: Since this one costs 25fps, I turned it off for the rest of the tests
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Add AI Airlines and GA (100%):

172: 70fps
Note: With Ultimate Traffic 2 on full steam, about 20fps, which I uninstalled

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Add airport traffic (100%):

172: 22 fps

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Add Cars (100%)

172: 20 fps

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Add Boats (both) (100%)

172: 18fps

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Summary: Thermal visualization, AI Traffic and High-End Planes are expensive in FPS. In my case, I can have everything maxed and leave out the thermals, and AI traffic and get a very nice experience. (I also back down my resolution to 16?? x 1080 for all the complex planes)

Informal and quick, but told me what I needed to know. Hope it helps someone looking to make things a little smoother.