Theres no "limitation" in bandwith, its just a number you get based on memory bus width and memory speed, so when you OC memory, you also get
better bandwidth.
12.1 is low with such big frequency, so either of 2 things happened:
1. claymore command to set frequency doesn't work (in that case, use wattman instead)
2. you forgot to change workload from graphics to compute in wattman
GL, and may the hashing power be with you

Thank you very much for your reply, Branko!
Ah, I see! Indeed, the Bandwidth goes up when the Memory clock goes up. Issue fixed

Regarding the low hashrate; You were correct once again! It was issue number 2: I had to change the workload from graphics to compute for each and every card. I just changed it for 1 card, as per AMD documentation it says:
Note! In systems with more than one GPU, this option will apply to all GPUs in the system (
https://support.amd.com/en-us/kb-articles/Pages/DH-024.aspx) But apparantly that is not true, at least not for my rig.
Once again thank you very much!!
I have same issue with you, how did you fixed? I can't see "GPU Workload" options on Radeon setting.