...I wouldn't buy an "ASUS GeForce RTX 2080 Ti ROG Strix O11G Gaming (11GB)" today when the new graphics cards from Nvidia or AMD come onto the market in the next six months!

In purely mathematical terms, this monitor has about 89%* of the number of pixels that a typical 4K monitor has, so an RTX 2080 should manage a good 60fps here, at least with DLSS 2.0.
5120x1440=7'372'800 pixels (here) vs. 3840x2160=8'294'400 pixels (4K), even a RX 5700 XT should still deliver a good 50-60fps here, but the 240Hz don't bring much or massive tearing could spoil the fun ;)