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In general, a given rendering setting in X-Plane will impact *either* the CPU or the GPU (i.e., the graphics card). Your overall framerate will be limited by whichever of those two is most heavily loaded.
So, my recommendation would be: check and make sure you're not bottlenecked on either your CPU or GPU. The rendering options portions of the manual should give you an indication of which settings affect the CPU versus GPU. Likewise, the section on tuning the rendering options for best performance may be of use---it will walk through turning down all the rendering options to start with, then slowly turning things up until you find the best setting for your machine.
This site is no longer being actively maintained.