The sliders people may be talking about is in the settings portion of flight sim.  These sliders can be adjusted to decrease or increase the ground textures and items, the aircraft textures, and the video settings.  The best way I increased my frame rates was to turn off multi texturing.  When you climb to altitude you won't notice the difference until you come down to the ground and even then it looks fine to me.  Pluse turning off the water effects is another way to gain frame rates.  You still see the water but it doesn't animate or have reflections.  This way the computer isn't worried about the unimportant things.  My planes still look good and the buildings look good, and in my opinion the ground looks fine.  I am able to keep the scenery at very dense and the dynamic at dense, without the suffering frame rates of the card trying to render every last detail.