For 4K gaming, I usually hover around 45-50 FPS average with all settings set on Ultra except for a few.
For example, I have AA (Multisample AA in the menu) set to none as it's not really needed at 4K because the sheer pixel density of my 4K TV makes AA not worth the performance hit as it's not much of a difference at this resolution. I also have Tessellation Set to Medium, Post Processing set to Low, AO set to SSAO and textures set to Ultra instead of Fade Touched. Last but not least, I have both cards OC'ed to 1250 core (boost pass 1400) and 7.5ghz Mem for stability and heat management.
These are the settings I use at 4K and the game look gorgeous, but to really appreciate all the eye candy and such, I set the resolution to 1440p and I'm able to crank up all settings to max and have about the same performance as my above 4K settings.
If I set all settings to max at 4K, my poor SLI GTX 970's manage to barely hit 30-40 FPS during normal gaming and dips below 20 during intense spell casting and such. lol.
I do admit, the XBOX 360 controller works perfectly with this game, what a shame that the keyboard/mouse UI is trash in this game, but I'm ok with the controller since it's not a shooter, lol.