MATX and OC? NOPE!
Yeah you're right, the gigabyte board, although you can OC alittle is actually has very limited BIOS options for overclocking.
Perhaps if you really want mATX, crossfire and overclocking you'll have to spend a bit more.
Read some reviews of the ASRock Z77 Fatal1ty Professional-M and Asus Z77 Maximus V Gene as I'm pretty sure both of these support crossfire and overclocking.