Go and install the demo, see how it runs. The settings/variables which will affect your framerate are:
- where you're flying (affects the baseline object density)
- rendering options
- resolution, (appears to be vid card dependent)
- anti aliasing (video card dependent, if I understand it right)
- texture res (if you exceed the texture buffer on the video card, you will experience stuttering as you change views while textures are moved from RAM to the texture buffer on the card)
- object density/visibility (these is where it ALL happens, these settings can run you from 125fps down to 19fps, at which point Xplane starts limiting your visibility with fog to maintain frame rate).
- water reflections (go for one or two from the max if you have a good video card. Only go for max setting if you have FPS to spare).
That's all that comes to mind right now. It's important to realize that some of the variables are video card dependent, and others are CPU dependent. Have at it!
Bear in mind, socal and ZNY are brutal on the system. The rendering settings that I use all over the country just don't work well in ZNY/ZLA.
It's worth taking the time to understand the rendering options, and to tweak for your rig. For the best experience, you want to shoot for the highest density of objects, and highest object visibility while still maintaining, say, 30-40fps. If you're getting 60+ fps, that's great, but you COULD enable more eye candy.