I am very satisfied with the Dell UltraSparp U2718Q, brilliant and sharp, I have owned it for a year. I also have a Dell P2415Q (24" - with 4K 3840x2160 resolution) as a second screen.
In the beginning I had a Full HD second screen with 1920 x 1200, this was very annoying. You can adjust the font and display size under Win 10, but it didn't suit me at all. That's why I also bought the 24" 4K screen. In retrospect, I have to say that I would have been better off buying two U2718Qs, then everything would have been visually consistent.

Conclusion: it is better to have two identical screens next to each other, at least two with the same resolution. Then everything harmonises perfectly. I don't know if the U21718Q is a good gamer's monitor (I'm not a gamer), but it's great for Lightroom.
It is also important that the graphics card supports two monitors with high resolution and the same refresh rate (min. 60 Hz). Check connections: HDMI 4K, or DP

I have been using the DELL UltraSharp U2718Q monitor for a few months and am very satisfied with it. I use it mainly for image editing but also for normal home office applications and really appreciate the high resolution. However, I can't say how suitable this monitor is for gaming. Spontaneously, I would think that using two monitors with relatively low resolution differences (3840x2160 v. 2560x1440) side by side should not be a problem.