This may help you:
When I enter my BIOS (I also have a Gigabyte motherboard), if I don't press CTRL+F1
before entering the M.I.T. section, then the only four selections available are the ones you should be changing. As I'm going down the page in the BIOS, it lists 5-5-5-15 on standard, and when I vary the option to Manual
so I can change these values, I am able to change these defaults to my timings of 4-4-4-12 (what my GeIL RAM is rated at).
So try entering the M.I.T. section directly - without entering any keyboard combinations first - and see if you only have those four available.
I would take a photo of mine so you can see, but the wife has gone on holidays to visit family interstate, and she's taken the camera.