Ive been looking at RAM for building a PC and I understand the difference between DDR, DDR2 and DDR3 but what is PC3 and PC3L? Can I mix them i.e. have two sticks of 4GB PC3 and 2 sticks of 8GB PC3L? Is one better than the other for gaming? I know very little about PC's and this will be my first build, help would be great, thank you