I have an Asus 21:9 29", 2560x1080, not 3440x1440 like the LG you mention (which I've considered). The extra width is nice, and the aspect ratio is perfect when watching movies, but I find I need more vertical pixels.

Instead of the 34", wouldn't make sense to just go 4K (3824x2160) and get it over with? You're getting more vertical AND horizontal pixels. Personally, I'm salivating at the Seiki SM40UNP (40"). Anything smaller at 4K resolution and you'll need display scaling, negating the size gain. I don't think my 2013 ultrabook can drive it at 60Hz, but there are apocryphal reports that I may be able to eke out 50Hz.