Why? Fog slowing down performance for you doesn't mean you can't run the rest on high. I've got a very weak CPU and before the update i played on High and haven't seen any significant difference in performance between Low and High at that time, now if i want to disabled the fog i'm forced to use Low even though i would be able to run the game in High just with the fog disabled.

Also, i'm really, really thankful for serving us this really major performance boost, in other games generally performance fixes only address issues for specific card series not the whole playerbase and its usually fixes for drivers that are fixed with newer drivers.