I am running a I7-3930k OC to 4.7, 16gigs or RAM, Titan X Pascal OC to 2050 on the core and +500 on the memory, running everything at max and getting 60fps, but dips, especially near towns, cities etc, I had drops to the 45 range (kind of rare). I did some testing in the big city and even if I change resolution to 1080p from 4k, I still get about the same drops. So I am thinking it is something else, not an issue of not having enough GPU/CPU power, if it drops about the same at 4k and 1080p there is something else going on.
I did try the no MSAA and No FXAA and it seemed a little smoother, even though the frame rate was not really changing, it seemed a little smoother, but not 100%. I hope Playground/Turn 10 are reading this thread because game is outstanding, they just need to fix the hick ups, which seem like it is more a frame pacing issue. I have run the same race over and over (the dune buggy/helicopter one) and I get the same slight drops to 52 or so when I hit the small town area right after going through the beach area, regardless if it is 4k or 1080p, even tried MSAA/FXAA on/off at 1080p and 4k, still same drops.
Hope a patch is on it's way for this.