New alignment will also help, but that needs v6.9*, these were my results:
https://forums.unraid.net/bug-reports/stable-releases/683-docker-image-huge-amount-of-unnecessary-writes-on-cache-r733/?do=findComment&comment=10142
* I found out recently that pools (and only pools) with the new alignment still mount correctly in previous versions, but it's unsupported, i.e., use at own risk.