The new 4TB Hitachi Deskstar 7K4000 hard drive is out (not just announced, OWC has them in stock and ready to ship).
OWC has graciously agreed to send me four evaluation units, so that I can test them singly and with RAID-0 striping. I expect to see them next week for review.
See my previous review of the slower 4TB Hitachi 5K4000 'Coolspin' hard drive.
Unlike the 'Coolpsin', the Deskstar 7K4000 spins at 7200 rpm, has a 64MB cache, and is aimed at performance users.