Your mobo supports large hard drives if its UEFI.
As long as you have Windwos 7, you'll be ok.
After you set the drives up in RAID, when you boot in to Windows, you'll se tthe drive up in GPT, not MBR, due to size.
Now, I don't know if you can install the OS to a 3TB hard drive. I'll have to check.
OS isn't installed on the 2x 3TB HDDs - got it on a SSD which were installed months ago
The 3TB is storage and want it in RAID 1 so it's backed up - that's what bug me + the 746GB problem (would be nice to know step for step to do)