Unfortunately no built-in benchmark tooling for either of them. The nearest to it would be something like a standard DCS quick action mission or MSFS airport like KSFO and a C172 on the deck. MSFS has a ‘Developer’ section in the Options / Graphics that you can use to enable a decent frame-rate counter - that at least tells you a breakdown of CPU vs GPU bottleneck.
Thanks for the comparison so far though. I would think that the advantage of the 3080 is sort of tempered a bit by the 10GB VRAM max vs the 16GB on the 6800 XT. If the O+ was supersampled a bit to higher resolutions it actually gets close to what’s needed for the Reverb, and both DCS and MSFS love having lots of VRAM available.