Do you monitor your FPS?
Nope. FPS is very important to me in multiplayer games though, and I use those settings in PvP etc. FPS hasn't been a problem so far.
In SP it runs completely smooth 99% of the time. Sometimes, very rarely, it stutters briefly. Doesn't seem to be any particular rhyme or reason to when it does that, sometimes it happens when just entering the desert area, but not always? Either way, for every 2 hours of no lag at all there's 5 seconds of micro-freezes (that don't even make it hard to control a vehicle), so that's fine with me.