Same issue for me, I'm on a real Mac Pro 5,1 2 x 3.46 6 Core Xeon, 64 GB RAM, GTX 1070 Graphics + latest Nvidia Web driver.
I think it has something to do with texture swapping.
It seems to happen when you turn or move quickly and have to load more textures in to memory.
Lower resolutions it is better, but that's natural as you'd have more texture memory available.
I'm not sure why it's running out of texture memory on an 8GB graphics card though, it would be interesting to see how much of the graphics card memory is being used at any given time, not sure if you can do that on OSX.
*Update - at 3480 x 1440 epic detail my GPU is using 423MB RAM, I suspect this is the culprit. I do have a 2nd GPU in the system that only has 512 MB RAM so I'm going to remove that and see if OSX is that stupid.
*Update 2, 2nd card removed, still only using 500 MB RAM max, jerky as hell.
*Update 3, looks like it may have been a red herring, a different activity monitor (iStats) shows 50% memory usage on GPU which is more what I would expect, still jerky. Its definitely loading things from disk I think