Windows Server 2012 2TB drive limit on 3TB drive – UEFI, GUID

Firstly you mean GPT vs. MBR, not EFI vs. MBR - one's a firmware, the other a partition type. The only part it plays in your question is that, in general, you need an EFI/UEFI firmware based system (rather than a BIOS based one) to boot from a GPT partition, although that can be worked around sometimes.

Anyway a few things, DON'T EVER USE RAID 0, seriously it's an appalling idea, even for testing, it's the sign of an amatuer. Now also DON'T USE RAID 5 ON LARGE DISKS, as for very dull math reasons if you ever have to replace a disk then you're almost certainly introducing unrecoverable read errors. So use RAID 6 or RAID 10, that's what professionals use.

Another thing you want to do is create an initial smaller OS disk or partition, do not create one big disk/partition for everything, always separate the OS from data, put the OS in say a 100-300GB disk/partition and leave the rest to your data (VMs in this case). I don't know the disk controller you have but hopefully once you've created your array you should be able to carve it up into logical disks to present to the system, it's at this stage that you should make this first smaller OS disk if you can, this will allow you to partition it using either MBR or GPT, then present the remainder of the array as a second larger disk which you should partition using GPT. This will get you where you need to be and allow for each expansion in the future.

Well, after much searching, experimentation, and general frustration, I have basically come to the conclusion that Hyper-V does not currently support UEFI guests, even if the Hyper-V server is running in UEFI configuration.

This seems to be supported by the fact that that recent builds of Windows Blue have what they call "Generation 2" VM's that include UEFI support, based on this article:

http://www.chris123nt.com/2013/04/23/windows-8-1-blue-build-9369-hyper-v-uefi/

Sad really that there's been so much misinformation about this floating about, with so many people insisting UEFI works for guests, but I can find no way to make that happen.

EDIT:

Since this question was asked, Microsoft released Windows Server 2012 R2, which supports the Generation 2 VM's, which do in fact support UEFI for guests.