It doesn't matter. Neither GTX 780 Ti 2-way SLI nor R9 290X 2-way crossfire are able to average 60fps on modern games at 4K HD, even games that are nearly a year old.
http://www.guru3d.com/articles_pages/gtx_780_ti_sli_geforce_...
And these cards are 600-700 USD each.
If you find your experience completely ruined by frame rates ever dropping below 60fps, you're going to find most of the newest games kind of a bummer.
The experience isn't completely ruined, but immersion is affected. It adds the GPU limitation as another difficulty factor in the gameplay. In twitchy games, the moments of maximum screen chaos are simultaneously those where you need to react quickly, and you are less likely to be able to react quickly if you're dropping frames.
> But I still generally don't enable anti-aliasing over 2x unless it's a very old game, because it still costs too much.
You probably won't need it at all with this monitor, so you'll hypothetically be able to get some performance back that way.