Am happy to be proven wrong, but am 99.9% sure that to run 3440x1440 or higher at 60hz or higher, you need DP 1.3 or HDMI 2.0 or better at both ends. DVI Dual Link (not that a new ultrawide would have this anyway) or HDMI 1.4 won't do it. They will manage between 30 and 50hz at that res which looks terrible.
If the 750Ti happens to have DP, there is a very good chance that it will work OK, but it looks like there are a lot of 750Ti (most of them possibly) that don't have DP.