what 2x4GB to buy

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To be truthful dont mix and match ram. Your going to run into more issues A)mixing two different sets, between timings, voltage, and the chips themselves can give you issues B) mixing sticks and filling all 4 slots, some boards just have issues with all four slots filled now your compounding the problem with unmatched sticks.

If it was me i would save myself the trouble and pick these up http://ca.pcpartpicker.com/part/mushkin-memory-997123f It gives you the 16GB you want and wont cause any issues. Ive been running Mushkin for around 8 years now and every kit ive bought has overclocked well above the specs that i bought them at.
To be truthful dont mix and match ram. Your going to run into more issues A)mixing two different sets, between timings, voltage, and the chips themselves can give you issues B) mixing sticks and filling all 4 slots, some boards just have issues with all four slots filled now your compounding the problem with unmatched sticks.

If it was me i would save myself the trouble and pick these up http://ca.pcpartpicker.com/part/mushkin-memory-997123f It gives you the 16GB you want and wont cause any issues. Ive been running Mushkin for around 8 years now and every kit ive bought has overclocked well above the specs that i bought them at.
 
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