Sounds like some folk are just jumping on the ‘new hotness’ bandwagon.
4k will be nice for desktop work, sure, but prices are way too high for my taste atm. And you are correct that you are going to need some upgraded grunt to drive one at native res for gaming. But, one great benefit of 4k is that you can still run your games at 1080p and have no real disadvantage as it is exact pixel doubling! Which should hopefully meant no (or reduced) crappy artifacts from the monitor’s inbuilt scaler!
I have 3 x 27’s on my main rig, but only one is used during gaming. I’ll admit I have begun to notice more aliasing in games than I used to, but my GTX560Ti is beginning to get a bit long in the tooth. That said I still manage to run most new titles at mid-high settings, including at least 2xAA or FXAA, generally in the 40FPS+ range. Your 7850 should be just a touch beefier than my 560Ti.
Movies will make no difference at all, since you’ll probably consuming 1080P content or below anyway.
I think you’ll be more than happy with a decent 1080 IPS panel. Though that said, with CES2015 just around the corner, it could be worth waiting to see what 4K stuff is released and what price points they begin to hit. If some nice 4K monitors appear in your price range, you may just get the best of both worlds - greater resolution for desktop workload, little to no disadvantage for gaming when running at 1080p and ready to rock when you get around to the GPU upgrade down the track.
Edit - whoops, just realised WQHD is 2560x1440! Silly me! I think the above is accurate, for me anyway - WQHD it too pricey for my taste and it will be tougher to drive. Playing titles at 1080 will not be ideal with WQHD as it will rely in the monitor’s internal scaler. I’d go 1080p or wait and see what 4K stuff comes out at CES2015.