Re: Question about RAM
First, mixing memory sticks is never a good idea. Different silicon, with different timings, command rates etc., will often cause all the memory to default to the lowest common denominator. It can also cause numerous other issues. Always use memory that's identical to avoid problems.
May I ask why you want to add more memory? 6GB is more than sufficient for most average computer users. You mention nothing about your OS???
If you're using a 32bit OS, you've already got more memory than it can handle.
HAF 932 Advanced / Corsair AX1200 / Asus Rampage IV Extreme / i7-3930K / H100 Cooling 4x120mm
16GB Corsair DDR3 / GTX 580x2 SLI + GTX 460 PhysX / SSDs Mushkin 240GB, Crucial 256GB, Crucial 512GB