NB. These tips are aimed primarily at users of VFR Photographic Scenery of England & Wales. Most of the suggestions 

• You don't need to use Anti-Aliasing with a screen resolution of 1280x1024 or higher. Turn it off - it is a significant frame rate eater. If you are using Anti-Aliasing with a screen resolution of 1024x768 or lower, try increasing the resolution if your hardware is capable of it and turn off the Anti-aliasing. You may well find you get a better overall effect and increased performance compared to your previous settings.
• There's no point having the Sight Distance set in Display Settings, Weather set at anything above minimum. Reduce it to 60mi/96mm. The photo scenery textures won't display at that distance anyway even with Extended Terrain Textures enabled (this is a restriction of FS2002/FS2004), and you're putting an unnecessary extra demand on your system for no benefit. It's very rare for real-world visibility in the UK to be this high in any case.
• Reduce visibility in your weather settings (World, Weather..., User Defined Weather, Customise weather...) to 20 miles or less. Not only will this help with performance, it also creates a much more natural-looking colour balance for the photo scenery textures.
• Reduce Global Max Texture size to High. This setting has to be High to display the photo textures at their maximum resolution, but setting it to Maximum will only benefit 3D object scenery and/or aircraft textures if the designers have provided very high res textures for them. The impact on performance is not known, but working on the principle of assuming the worst, it is best to opt for the required/safe setting at least until safisfactory performance has been established.
• Setting the filtering to Trilinear may incur a performance hit for little or no significant visual benefit, particularly at 1280x1024 or above.. Try setting this to Bilinear, but once you've achieved satisfactory performance, try adding Anisotropic Filtering via Control Panel, Display, Settings, Advanced, GeForce xxxx, Performance & Quality Settings. Try 2x or possibly 4x if it's not too much of a performance hit. This will give a better result visually than trilinear filtering.
• With FS2004, you must set MIP-Mapping to 5 or above for the photo scenery. FS2004 handles MIP-Mapping very differently to FS2002. FS2004 allows settings of differrent amounts of MIP mapping, so the effect can be easily controlled, whereas FS2002 has  a simple MIP-Mapping on/off switch with a fixed amount of MIP-Mapping applied. Experiment with the FS2004 MIP-Mapping quality via Display Settings, Hardware until you are happy with the performance/visual quality.  With FS2002, it is recommended that you leave MIP-Mapping turned off unless you are happy with the resulting middle-to-far distance mush. Advanced users may wish to explore the possibility of fine-tuning the MIP-Mapping via the graphics card drivers or using third party graphics card tuners.
• Reduce the global weather settings via the drop-down in Display Settings, Weather. You can always increase the weather settings once you have achieved satisfactory performance, but higher weather settings can have a very significant impact on system performance even with high end PCs. It is a big mistake to assume that your brand-new high spec PC can handle anything you throw at it - it can't!
• Reduce Air Traffic Density in Settings, Traffic to 0% until you are happy with the scenery quality and performance. If you want to see other aircraft in the sky, try increasing the traffic percentage a little at a time while watching out for any negative impact on performance.  If you are concentrating on a particular task which requires maximum concentration of resources, e.g. advanced helicopter flying or flying fast through scenery, set the traffic density at zero, at least for the duration of the task.
• Going against the grain of the other suggestions, the final tip may actually decrease performance, but typically only slightly on today's PCs. Set Terrain Mesh Complexity to maximum if you wish to get the best out of any add-on terrain mesh scenery you may have on your system: . Many sites advise a reduced setting, and you are free to follow this advice, but be aware that any reduction loses detail in the mesh, which may affect your appreciation of the photo scenery.
•