The 8K Plus is going to have a lower ppi than the Reverb. If reading gauges and dials is important to you (it's DCS after all so it probably should be) then the Reverb is going to be unmatched.
The 8K X, assuming it ever comes to market, will match the Reverb in PPI so you should get a similar if more taxing experience with a wider field of view.
If by XR you meant the 5K XR, it is going to have a visual fidelity experience similar to a Samsung Odyssey or Vive Pro. Tolerable but less than ideal particularly given the price.
IMHO, image clarity and spotting > immersion from a wider FoV. I'd like both and the 8K X may fit the bill but until then I'm happy with my Reverb.