All the payware alternatives - REX, Active Sky etc, offer different resolutions. But the problem may not be the textures but rather the `mix'n'match` of different texture sizes. If everything is the same size you ease the calculation burden on the GPU substantially. It doesn't have to be lower texture res either - I can get better fps from using the HD FTX 2048 textures for the Mooney and Cessna with the 2048 clouds.
In any case you can reduce the texture size with a single stroke - reduce the Global Texture Complexity slider from full right and you reduce ALL textures from 1024 to 512.
