MacPro4,1 Nehalem internal SATA recommendations

I need some advice on internal SATA drives for my MacPro4,1 Nehalem.

Looking at the following for samples:

Seagate Desktop SSHD ST4000DX001 64MB 4TB 3.5"
HGST Deskstar NAS HDN726050ALE610 128MB 5TB 3.5"


Current setup:

Samsung SSD 840 EVO 500GB system drive
Hitachi Deskstar 7K3000 HDS723020BLA642 2TB project drive
2x Seagate Barracuda ST3000DM001 3TB sample libraries

I want to be able to run this machine with PT12HD for a while if I choose to upgrade after all ;-)

Thanks in advance!

MacPro4,1 Nehalem internal SATA recommendations