Yeah 6800xt seems to be best at 1080p, 1440p single screen and VR (don't include high resolution headsets like the G2 in that though) for simracing. Its probably an acceptable option for ultrawides as well but i've not seen tests yet. But for triples its not as good as a 3080. Memory capacity isn't the issue I think its more the memory bandwidth which is the bottleneck, 3080 and 3090 have huge memory bandwidths. 6800xt uses 256 bit memory bandwidth but compensates with a very fast cache system on the die.
Because of this generally 6800xt looks like its rasion d'etre is being a killer 1080p and 1440p esports card for FPS shooters when you want 200+ fps.
I think a 6900xt will be more of the same, its got the same memory bandwidth as a 6800xt but more CU processors. It'll be an improvement for sure but still not enough for triples, like it'll be a 6800xt and just excel even more in the 1080p and 1440p single screen performances.
Another issue is supply of 6800xt is looking pretty grim right now, worse than the 3080 at launch, there is talk of stock mid december but no promises. None of the suppliers have said when there will be any stock at all. I'd keep the 3080 preorder tbh. If you want to gurantee a GPU before Xmas a 3090 looks to be the only real option right now, but you are paying a premium for not very much of an improvement.