Shadowsport - many thanks for you response.
I think you are looking at Rev 2.0 - the link you gave is Rev 2.0 - FG1 is for Rev 2.0
My board is Rev 1.0. I have F8L BIOS installed - the comments for F8L say support for 3T+ HDDs. However it doesn't say Support for 3T+ HDDs in RAID mode. It does indeed support 3T+ drives in IDE mode, but as soon as I set RAID mode it reports the drives as 746GB.
The board is 4 years old now - doesn't time fly! So my guess is that Gigabyte are not keen to spend too much time on BIOS upgrades for it. Can't say as I blame them.
Anyway, good excuse to upgrade - I have purchased a GA-Z87X-UD5H rev 1.1, i7, and 16G of memory. I'm assured that supports 3T+ HDDs in RAID mode. We shall see.
Roy