All ZFS values like record size, compression, etc. aside from sync=always are FreeNAS defaults. The guest OS was a stripped-down Ubuntu VM, which defaults to ext4. I know that the data has hit the physical storage only as much as I trust the vsphere/iscsi/zfs chain. I'm not convinced that the benchmark is very valid at all, esp. considering compression. But it was able to uncover a "terrible" vs. "good" performance.
One thing that I did notice was that the SAS3 HGST Ultrastar seemed to be a touch faster than the SAS2 Zeusram with the above silly benchmark. But in practice, I suspect that no difference would be noticed.
I did test out a local-only dd experiment, but we've had some hardware issues that have distracted me in the meantime.