The WD Ultrastar DC HC520 / HGST He12 should have a transfer rate of 243MiB/sec.
This is true for the first two TBs, but than it degrades to only 50% in the center of the drive.

Used the…

WD Ultrastar DC HC520 / HGST He12 50% slower in the center

Source: [H]ardOCP – WD Ultrastar DC HC520 / HGST He12 50% slower in the center