This is quite subjective, and likely very system-dependent. FSX is relatively insensitive to some settings, and hypersensitive to others.
Graphics
Target frame rate: seemingly even more so than FS9, FSX will effectively use cycles not absorbed by refreshing the display. So set this as low as you can tolerate it to reduce blurries and have scenery elements display properly. Some folks are claiming better performance with frame rate set to unlimited though, so experiment for yourself.
Filtering: if your video card has anisotropic filtering, select this and check anti-aliasing.
Global texture resolution: I didnr17;t find this made a huge difference to performance. Set to Very High
Lens flate: minor impact but every bit helps so I turn it off
Light bloom: high impact, itr17;s off
Advanced animations: unsure of the effect
Aircraft
Aircraft shadows on the ground: off
Aircraft cast shadows on itself: off
Aircraft landing lights illuminate ground: on
Scenery
Level of detail radius: I have this set to Large as it seems to make very little difference. But experiment on your system
Mesh complexity: 92
Mesh resolution: for most purposes 38m is plenty, 19m only if you have addons that need it.
Texture resolution: surprisingly this doesnr17;t have as much effect on frame rates as I would have thought. If you want to experience higher-res textures, go to 2m. 5m is equivalent to FS9. Likely the impact is mostly on the blurries, as the sim has to load more data.
Water effects: this setting does affect my performance much until I hit Mid 2.x, which is where water reflections kick in. Then frame rates drop dramatically. So generally I have mine at Low 2.x.
Land detail textures: on
Scenery complexity: I have mine set between Normal and Extremely Dense. It is indeed a sparse world in some areas at Normal! The effect this has will vary drastically with how many custom buildings are placed in the area, and what complexity theyr17;ve been assigned by the designer. Near CYVR, I get a 30% increase in frame rates dropping to Normal.
Autogen density: certainly anything above Normal is asking for trouble. Ir17;ve been trying autogen off in an attempt to get flyable performance. With the higher resolution ground textures, this looks much better than in FS9 with autogen off, but is not much good at very low altitudes.
Ground scenery cast shadows: no
Special Effects Detail: high, doesnr17;t have a large effect. I imagine this would vary with the number of effects active
Weather
A pleasing aspect of FSX is that the weather doesnr17;t have as much of an effect on performance as it did in FS9.
Cloud draw distance: 96 km
Thermal visulization: none
Detailed clouds
Traffic
Airline traffic density: varies drastically with the amount of traffic you have in your area. Your17;ll have to play with this one.
GA traffic: ditto
Airport vehicle density: minimum
Road vehicles: this has a very high impact if you have a lot of freeways, so I set it to 4%, just to get a taste of activity, or turn it off
Ships and ferries: there are few of these, and it doesnr17;t seem to have a high impact so I have set this to 100%
Leisure boats: again, I give myself a taste at 4%, the impact is quite high if you push this slider up, assuming therer17;s lots of water around.
