I ran standard beta with 4K with a single GTX 560. I got around 35-50fps outside stations, around 20 inside. This is acceptable for someone who's used to console gaming, perhaps less for those playing PC games at 100+fps.
I was seriously considering getting a second GPU come launch, but decided to try the game on my 86" projector screen at 1080p. Haven't looked back, getting your entire field of view filled with vast space is immensively satisfying

It has the added benefit of being able to play on a couch with surround sound, as my computer corner only has 2.1 sound.
Haven't tried in gamma or after launch, but I'm pretty sure it would work very well with dual GTX 560.
Full computer specs: CPU: Intel Core i5 4570 RAM: 32GB GPU: nVidia GeForce GTX 560, dual SSDs, etc.
its really not worth putting up with the UI problems in windows.. unless you like micro text in everything other then gaming..
It depends. It is mostly a non-issue in Windows 7 for me: you can scale text up to acceptable size, and browsers scale text as well. Viewing photos online can be frustrating as they aren't scaled. Windows 8 is supposedly even better.
Photoshop has UI and icon scaling, finally. Don't know about other software, but yes, if you rely on something that doesn't support UI and text scaling, it can be frustrating.
I use my desktop mainly on Linux Mint for everyday use, and it's a non-issue there.
4K would half what you get at 2k resolution. I have 60FPS inside the station at 2560x1440 on GTX Titan. 4k DSR makes it 35FPS inside the station.
2560x1440 is not 2K, but 2.5K. With 2K (i.e. 1080p or 1920x1080), you would get
quarter the performance with 4K. 4K has four times as many pixels as 2K, and around 2.2 times 2.5K.
Pure fps calculation is a bit more nuanced than that due to memory bandwidth etc., though. Also, you can turn AA down or turn it off altogether, as it is largely unnecessary with the high DPI of 4K monitors. That alone can improve fps by 10+. Haven't bothered to make a comparison of 1080p and 4K fps on my system.