There are games that might do 1080p30 or possibly 4K30 (Destiny 2) and some that'll only do 1080p60 (Ark, which apparently is sticking with 1080p30 on the PS4 Pro) but the majority of devs that have spoken have said they had it running 4K60 within hours of getting a devkit.
The Titanfall 2 devs said the machine runs their game at 6K and downscales, or something like that, so I would have a hard time saying it's not a true 4K machine.
As to the CPU most of the graphics are done on the hardware command processor on the GPU, not on the CPU so it should be far more than capable. I'm going to have a hard time coming back to PC gaming unless something absolutely **** amazing happens in the next few years.