I have a a Gigabyte EX58 UD3R and I have a pc3-10666 1333MHz 4 gb 2x2 kit (7-7

This memory that you are looking at is Dual Channel ram, which may not work with your current config. Triple Ram sets is what you are looking for and they come in 1 or 3gb or 6gb or 12gb sets. Triple channel generally requires 3 sticks of equal size to make sure that they work at an optimal speed.