look, ultra settings is a bit tricky, in games like crysis 3 and metro last light anti aliasing is so demanding that on MAX anti aliasing in both these games i doubt and single gpu would maintain 60 fps even on ur resolution.
but, lets ignore antialiasing in crysis 3 and metro last light, and maybe some other VERY demnading fetarues( there arent many) that you can give up on, on ur resolution, which is considered quite low for todays standarts and what high end cards are capable of, i would say a gtx 760 is a good option, and will perform VERY well in games and well allow u too max out and get a smooth experience in almost anything.
if u do wanna go overkill, and be safe more for maxing out future games, maybe consider getting a 770( even though again, i would say that's overkill for ur resolution.
you have to understand, there is no limit, you will benefit from any card, or even dual cards, but you have to set the limit.