I’ll add that every SMB connection remains single-threaded for now and that I manage to max out a single core with SMB every time I do heavy transfers to backup. Thus, a high clock speed / high single-threaded performance is key to not bottlenecking a 10GbE system, even if it relies on HDDs in its VDEV(s).
My NAS’ CPU is limited to 1.7GHz, the more file-server oriented version of my motherboard (uses a 2-core, 2.2GHz D-1508) at 1/2 the cost would almost certainly be more performant re: running as a simple file server than the 8-core D-1537 it has. If I was more skilled, I would perhaps even attempt a $60 CPU swap.