Simple answer is no. The VRAM is there, but I will tell you my old 670's would not stand a fighting chance. Unless you plan to drop IQ settings to lower settings(and what fun is that.......) then I'd shy away from 4K. 1440p you will probably fair "okay" , however who knows what future game titles will be like. I always considered my 670's as a perfect 1080 setup. Not sure I'd put too much more faith in them in today's world though espiecally trying to run 1440P & up.
 
P.S. AMD is rumored to be lowering the prices on their 290X cards in light of the 970 drama going on. That would be a great buy at $300. For less money though, and it's just an opinion, their really isn't a lot of cards I'd trust for 1440P & UHD accept the GTX 980, GTX Titan(s), GTX 780(ti) 6GB, and Radeon 290X. And for all of which you would want 2!

The GTX 760's 4gb SLI should handle 60FPS without noticeable dips at until 1920x1200 from what I know. It helps to have windows 8.1 and a recent intel cpu with atleast 8gbs of ram. 
 
I ran Unigine Heaven Benchmark 4.0, Settings 1920x1200 8xAA Fullscreen Ultra Extreme and got the following results-
GTX 760 SC 1215core 1725mem FPS 31.4 Score 792 Min FPS 13.9 Max FPS 70.7
GTX 780 SC 1215core 1710mem FPS 57.1 Score 1438 Min FPS 18.5 Max FPS 121.3
 
The asic score on both were almost even hence noting their similar max overclocked numbers. The stable overclocking I got on the 780 was on par with most stock clocked GTX 780 Ti's only the Kinpin might be faster. I temporarily had the 760 2gb SC ACX but the blower titan style 780 was perferred for my case and was almost two 760s when OC'd, you should be right their with 780's 970's and 780 Ti's. But I like how you said gotta have 60FPS without dips. Thats important when things are blowing up like for example your carrying the bomb in a tank in Obliteration and you need to react quickly.    
 
 
 

I run one gtx 760 at 4k with 30+fps and looks decent I have a new gtx 760 to arrive tomorrow and it will surely run 4k at 60fps on sli.

I'm running 2 760sc in SLI with an HP envy 32 monitor which is 2560 x 1440. And playing Assassins Creed unity I run 60FPS. In WoW I also run 60FPS except in very high Pop areas. Then it dips down to mid 30's to low 40's.