First, know that your overall frame rate will be limited by either your CPU or your GPU (your graphics card). It's very possible that your CPU is much more powerful relative to your graphics card, or vice versa. In such a case, you could hypothetically turn the CPU-heavy features up much higher than the GPU-heavy features (again, or vice versa).
The left half of the "Rendering Options" section contains the GPU-heavy features: visual effects, texture quality, antialiasing, and shadows. Likewise, the right half of the Rendering Options is the CPU-heavy features: world objects, reflection detail, and parked aircraft.
Here are our steps for finding the best compromise between performance and visual quality. Start with all sliders at their minimums, and all checkboxes off. From there, I would turn up the settings in this order:
1) CPU side: Go to a big airport with lots of 3-D objects, like KSEA, enable the parked aircraft, and start turning up the number of world objects and reflection detail. Eventually you will hit a point where your frame rate drops lower than you would like, and at that point, you'll want to back off a step. Note that the effect on your frame rate from the number of objects and reflection detail are very much cumulative: if you have minimal objects, you might be able to max out the reflection detail, but as you add more objects (giving X-Plane more things to calculate reflections for) you'll need to dial down the reflections.
2) Texture quality: Having found the number of objects you want to use, start bringing the texture quality slider up. Note that you'll need to restart X-Plane (and go back to KSEA) for changes to take effect. If the size of the loaded textures ever goes beyond your graphics card's VRAM, you'll see a sharp drop in performance, so for safety's sake, I suggest leaving some "padding" here. (Since different airplanes and different scenery packs might need more VRAM than your test area.)
3) Other features on the GPU side: I'd suggest increasing the Visual Effects slider first, and only increase the antialiasing or scenery shadows if you get it to a point you're happy with and still have higher frame rate than you need.