Few ideas that jump to mind:
What thermal interface did you use?
Possibly need to reseat cooler.
Use the monitoring tool to see if all four dies have all engines enabled
My gut is gunna say one of the first two lines since for those temps at that speed seems odd
I have used the stock coolermaster, AS 5, and Artic Alumina (ceramic based). The Alumina is on there now. I did that earlier today.
The monitoring tool shows all 4 dies running... but I don't see a section that shows info about the engines.
I'd look at seating the waterblock again. My best results came with the block finger-tight plus a little(~1 turn). Cranking it down got me higher temps.
With tons of air through the rad and tons of air on both sides of the board, you should be able to push it up.