Nobody ever said your sceneries have lower fps then other developer's. It's usually the opposite. An usual mistake, is to compare different airports in different places, without taking into account:
- The scenery around the airport. For example, KLAS has a very detailed city very close to the airport, while OMDB has a desert around it, and TJSJ has nothing except sea.
- The AI planes. If you want to judge the fps an any airport, you should always test it with AI set to 0%, otherwise you are not really testing the airport, but the AI.
- Setting the fps to 40 doesn't make any sense. Some might find useful to set the fps to integer fraction of the monitor screen refresh (usually 60 hz), so it should be either 20 or 30. 40 will make for a jumpy fps. And, in general, it's best to use an external fps limiter, if you really want to use one, rather than the FSX internal one.
Also, you should never set the fps limiter if your fps is already lower than the limiter, because it will lower it further. The whole point of the FSX fps limiter, is to not waste cpu time to draw too many frames IF your fps is MUCH higher. So, for example, if your fps was 80, it might be worth setting the limiter to 60 (because your monitor won't refresh higher than 60 anyway), or 30 or 20.
But if your fps is lower, ALWAYS set it to "Unlimited"