it looks like rev. 6.6 should be the only rev. for your model. otherwise the gigabyte spec page would have links to the other rev.'s right next to the model # at the top of the page.
even if it doesn't matter what rev. your board is, and you're just really paranoid or something, you can open up your case and take a look for yourself. on gigabyte boards it will have the rev. # printed at the edge of the board, on the bottom-left hand side of the board.
here (inside the green square somewhere),