Got this monitor yesterday, hooked it up last night and...holy shit. It's almost as revolutionary as going from software rendered Quake to GL Quake on the 3DFX Voodoo 1.
Are you okay with the framerate hit you'll be seeing at 4K?
http://www.digitalstormonline.com/unlocked/nvidia-gtx-titan-black-sli-4k-benchmarks-idnum175/
http://www.anandtech.com/show/7120/some-quick-gaming-numbers-at-4k-max-settings
Thanks for the info - I think I'll use my killawatt to check what going from one 290x to two 290x's increases the wattage by and then decide if I should add a third 290x or get a new PS based on that.
I've picked up three refurb 7970's for $229 from NE in the last week or so. Lately they've jacked the price up a bit to $259 though so not as attractive.