I have an XFX Speedster MERC 310 RX 6900 XT black gpu and have found that while playing games, primarily BF3, that my GPU clock is running half of its rated speed with syncing disabled. Even in benchmarks like Time Spy the gpu clocks are well below spec while my power and temps are fine. My case has great airflow so my gpu temps never go much beyond 130° F while gaming while my gpu is only slightly warmer.
I replaced my power supply with an EVGA Supernova 1300 G2 just to be sure since the other one was 7 years old with no change in behavior. I am running the latest drivers via adrenaline on windows 21H1 but the behavior was also present on 20H2. I did send a report to AMD but haven't heard anything back from them.