Here's my current settings. I fly in VR with a Reverb G2 and a 5800x CPU along with this 6900xt. Major points:
1. I don't need 100% fans to keep GPU cool enough. 75% keeps the hotspot temp below 95C. Note the card is good to 110C so this is well within acceptable limits and keeps the noise reasonable.
2. The card runs hotter if I move the min freq higher without any noticable improvement in performance, so I leave it at default 500.
3. Increase the max frequency although anything over 2650 doesn't have an impact as the card can't get enough power to hit higher speeds. Note you can increase the power limit of the card using MorePower Tool but it has very little impact on actual performance so I don't use it any more.
4. Lowering the voltage too much causes stability issues. I find 1140 works for me.
5. Upping the memory speed too high causes stability issues so just increase it a reasonable amount.
6. I tested with smart access memory on and off and don't see a difference, so I leave it on.
Good luck. I like this GPU a lot. It performs great at a reasonable cost compared to Nvidia solutions.