I currently have the Gigabyte GA-970A-UD3 -- AMD 970 motherboard, and have 8 GB [4 GB X2] DDR3-1600 Memory Module - G.Skill Ripjaws X. Can I fill the other 2 ram slots with two 2gb sticks? Do they need to be all the same speed? Any information is welcomed, thank you. Running Windows 7 Home Premium.