I am perfectly happy with my 6900xt. Running it at 220w limit which still manage 20k graphical score in Time-spy. The trade-off was 10% performance vs 350w for 37% power reduction and roughly 5% performance lost vs 300w for 27% power reduction.
Previously was running tuned for 300w but have since switched to 220w for good. Performance lost in game is not noticeable but the reduction from 220w-250w max power draw to 150-170w is huge. PC is completely silent and i can game alot longer without having to turn on the AC.
7800 XT is a good purchase since it is pretty much a better version of 6900xt out of the box. (Not comparing with those xtxh 6900xt that are throwing away power efficiency for that additional 10% performance vs running at 350w limit.