The Dell U4021QW is probably the best monitor I've ever used. I, too, got sad with 1440 vertical pixels on previous ultrawides, so I was pretty excited when they announced this one. 5120 x 2160 is really a dream. It's limited to 60hz, which bothers some folks, but I haven't noticed. I don't game or anything on it, though.
I actually forgot that that monitor configuration existed. It looks nice, although I assume you would still be running at the same UI scaling as a 1440p monitor, and the higher pixel density compared to a 34" ultrawide 1440p display (around 25% higher) means you put the monitor closer to your eyes. So unless you're doing non-integer scaling (which I want to avoid if at all possible), you get a lot more real estate than the 1440p display, but not 2x density. Or you could do 2x scaling, but then you've just got the real estate of an ultrawide 1080p display. Personally I have plenty of real estate with 3440x1440, and what I'm really interested in is jumping to 2x scaling.
