According to Gigabyte only the Revision 3.3 boards (DS3, DS4 & DQ6) will be 1333MHz compatible.
The last but one BIOS release for each of the boards listed above said:
1333MHz FSB Support (Rev. 3.3 Only).
Quite how the BIOS update will be able to tell which revision of motherboard it has been installed on I don't know - but that is the official line from Gigabyte.
I too currently have a Revision 1 DS4 - if it ever runs with a 1333MHz CPU I'd class that as a bonus, not going to rely on it.