Going to have to lower your expectations there. I have a similar set up, GTX 770, i5-4570, 16GB RAM, SSD, etc. 60fps usually, but crowded areas will always give you less than 60fps. Markets, for sure. Just wait until you get to Revenant's Toll.

Like I said, though, the majority of the game runs at 60+fps, it's just these areas it happens. Nothing you can do about it, that's just how the game is.