i have two 2 gb ram sticks at 1333mhz of the same model and brand, and a 4 gb 1333mhz of a different brand, i was using the 4gb and one of the 2 gb to get 6 gb of ram, but i read that using 2 ram sticks of different brands can cause lower perfomance, so now i'm using the 4 gb ram (the 2 gb ram...