I have noticed when playing the game and looking at screenshots that the topmost cloud layer appears to be rendered twice with one layer slightly offset. Not only does this look a little odd (to me it does) but could it be using precious FPS?
If you look at Lewis Bloomfields post here
you might see what I'm talking about. His first picture with the Spit. If you look just above the Spit you may see the ghosting of two cloud layers. This is not the best example to illustrate this and I don't have access to my PC to get screenies to illustrate it better.
If you get a chance have a look up when in your cockpit, or look at the clouds high up in 'replay' mode, it does appear that the cloud layer is duplicated and offset. This is not evident on the official screenies (I don't think) but is clear to see in game