Does the scenery perform faster when using the HD textures option because there are less textures to be loaded? I know they take up some VRAM, but I would like to know when the scenery will perform faster in terms of fps (with or without the HD textures).
There's no difference in fps, if you turn the HD textures option on/off, just in VRAM (and RAM, under DX9) allocation.
The advantage in fps of using 4096x4096 textures, the way we use them (not to get higher than normal resolution), is compared to an hypothetical version of the same scenery, made using the same texture data, but divided into many 1024x1024 textures, compared to few 4096x4096.
For example, KLAX uses only four 4096x4096 textures for the photoreal background, while KDFW uses 58. The overall space taken is not much different ( 4 4096s equals to 64 1024s), but KLAX objects can be rendered faster because it has less drawcalls and less changes of materials.
But once the scenery is made that way, changing the resolution in-game won't make any difference, except for the RAM/VRAM usage.
