I've noticed that in the spawn of surf_andromeda my FPS drops way down. But when I'm surfing in the cave it goes back up. I think it has to do with the fog when you look all around. I asked if anyone else had the same problem and a few people say they do too.
I'm not sure if this is the fog causing this, it may in-fact be helping. There's a lot going in at the spawn of Andromeda, a lot of high-res textures, the area is also very large, as well as that high-res skybox. I could be wrong but the fog may be added to hide some of it as my FPS doesn't drop as bad as say Squirrels which has none!
Yeah, this is a really tricky one in terms of actually knowing what's going on and what's causing you net benefit. The risk with removing it is if it does cause more issues it's tricky to find out because my PC has no issues at all. I'll do some testing and see what I can come up with in terms of stats to see what may or may not improve the overall framerate for that map.