assatm: its a bit hit and miss to be honest, most of the time its down to the game being programmed badly. I find that if you wait 3 months after launch and then play the game your experience is much better than if you try and play it before then. Some games work well on launch day.
In terms of micro-stutter well I can say that at 4k the 980 has micro-stutter all over the place. Generally, I don't see this in two card mode at 1080p or 1440p unless the game is to blame i.e. a ubisoft product. I personally think that the general poor 4k perf. on the 980 is down to the memory bus being limited to 256-bit. 1080p and 1440p perf. has been stellar.
I think the TX's larger bus and extra vram legroom will help solve these problems.
G-sync was made for 4k, its a shame that TV's don't support it.
I blame it on AMD !!!!!
Going back a year if a game was a Gaming Evolved title you could near enough guarantee that NVidia would go out of their way to make sure it had fantastic SLI support. Now that AMD are a bit off form it seems NVidia are not bothered either. Having said that it could be just my imagination.