For what it's worth, I just happened to do quite a bit of frame rate testing last night to see how the latest update runs. I normally run vSync so started of course by turning that off. I tried DTM 14, DTM 13, and R3E with a couple cars on 4 or 5 different tracks. I was surprised how well everything ran (100-140 FPS) so I bumped up most if not all of the graphic settings and still was able to maintain a minimum of 70 FPS but things were not completely smooth until I turned on vSync which is the way I always run this sim (actually all of my sims). So far I'm impressed with the graphical performance.
So, not any help to you but I am also running a GTX 780 currently at 2560x1440 (triple screens down for the moment).
I would check for background processes... if I run into anything I will post what I find.