That datasheet is from when we first released the RN312.
The WD RED 6TB WD60EFRX is on the list (http://kb.netgear.com/app/answers/detail/a_id/20641).
Do you have a different high capacity disk in mind?
The issue with some high capacity disks can be screws in unusual positions etc.
Not all drives are equal, but in a 2-bay you may be able to get away with more than you would with models with more drive bays.
Wow, there are 10TB drives available now. Amazing! One of those 10TB disks would cost multiple times what the RN312 cost though.