This issue is obvious and I'm pretty sure that you know about that. While considering performance issues and low FPS I think you should rewrite LOD algorithm. While playing in huge city locations like Chernagorsk or Dubky frames drops to ~30FPS on pretty good hardware (i5-4570s, R9 280x, 8GB RAM, SSD) while in wilderness it is ~ 80-120FPS.
I think the main problem is Level of Detail. As every LOD algorithm yours should replace original model with low-poly one when player is far from the model (object or building). DayZ LOD seems to be broken, because I often see that textures are "blinking" which means that there are two 3D models on same place (take a walk in Elektozavodzk and look at windows). This way LOD makes performance even worse. What more sometimes, while character is standing in place, LOD is constantly swaping high-poly and low-poly model or coming closer makes LOD to load low-poly model (really noticeable while walking to the building which has opened doors - low poly model has always closed doors). I think that main reason of low performance is poorly written LOD algorithm. AFAIK this issue is exactly the same one that occured in Arma 2.
To prove that this algorithm is broken I lowered scene complexity setting in config file. No performance gain, just worse quality (more flickering).
While looking at objects really far (like standing at Balota Aiport and looking at skyscrapers) they look really flat. You could use some post process on them to make them look better. (bump mapping with decent texture maybe?)