All you need to do for 4K resolution is use the HDMI port. At least from the specs. I don't have a 4K monitor, so I can't test it.
The 680 is a great card for that. The 690 can only be used 50%, because it is a dual GPU card and PR can only use one GPU, so is a waste of money for PR and your intended use.
Wish I could test it - but I am in the same club as Harm - no access to 4K monitors.
Yet if it says so in the specs, I have no reason not to believe them.
On a side note: if the 4K panel you are planning to get supports 10-bit color, and you want that support, go with Quadro K5000.