Mixing and Matching Ram

Solution
If they are exactly the same standard, latency,voltage and frequency they will work but it is not recommended. Best case would be to buy the exact same model again.

What I recommend is a complete matched set for ALL the ram (no mix and match) for ultimate stability and performance.
If they are exactly the same standard, latency,voltage and frequency they will work but it is not recommended. Best case would be to buy the exact same model again.

What I recommend is a complete matched set for ALL the ram (no mix and match) for ultimate stability and performance.
 
Solution
gskill are better so even if you manage them to work you will need to loosen gskill timings and lower mhz to much corsair's specs. moreover you will lose dual channel support since corsair isnt 2x4gb but a single 8gb stick. (dual channel only work on pairs) i would only run the gskill. if 8gb isnt enough for you better get another exact pair as already suggested.!