I'm using 2560x1440 IPS panel with 2 TX in SLI
and they crush every game I have .........

+
21:9 3440x1440

Yup what he said ^^^^^^^

It really depends on what you want to do with it and what your priorities are!  If you want max resolution you can go the 4K route, but this does come with the drawback of some scaling issues in Windows.  It's definitely better in Windows 10 but still not great.  Otherwise, you could look at 1440p but with a fast refresh rate?  The 34" super-wides are also great, if you have the space.
 
I went for a Dell S2716DG for my set-up, it's a 27" 1440p 144Hz monitor with G-Sync.  I'm only running 780 Classifieds in SLI at the moment but have a pair of 980 Ti Hybrids on the way.  I didn't want the hassle of 4K, and to be honest didn't think the jump in fidelity was worth the performance hit compared to 1440p.  Also my old monitor was a 144Hz 1080p panel, and any 60Hz monitor just doesn't feel right to me now.  G-Sync is a nice bonus, too.
 
With all that said, the monitor market is a bit of a lottery right now - not sure what has happened but the QC at many companies seems awful.  You pretty much take a gamble with any monitor you buy!

rauf00
IMO no.1 advice would be seasrch for g-sync/free sync. This plus >75Hz really do the job.
At first i've got single Asus ROG Swift 1440p/144Hz 1ms lag NT panel, which is amazing so took another 2. Which is even better as triple combo for simracing games.
Now i got new Acer Predator X34 3440x1440  upto 100Hz refresh with g-sync, hard to describe how good it is. Honestly i can't stop playing ;)
 
PS just be sure to check oc.net where few folks had some problems (bleeding, wake up function, problem with OC), mine was perfect.
 

 

 

 

I too have this monitor with a Titan X SLI setup.  It is a wonderful monitor.  I have zero problems with it.  It seems most of the monitors that have problems are in Australia and Europe.