Mixing Ram Types- Does this matter?

[TheoSqua]

So I know just enough about RAM to be dangerous. I have a laptop with 4GB of RAM. A friend upgraded their year-older macbook to 16gb of RAM and had an extra 8GB stick left over.

I looked up the RAM and saw that my laptop and the new RAM were both DDR3 running at 1.5v, my ram being a bit newer ran at 1600 vs 1333 for the old RAM, but I figured running at a slower frequency would be worth the trade-off of tripling my ram for free.

I installed the RAM into the extra slot on my laptop and booted up no problem, i'm working on the computer now with 12GB of RAM. I loaded up CPU-Z to look and noticed that the original RAM in my laptop is running at 1.28V, even though it's specced at 1.5v, and the ram I just installed is running at 1.5v. Does anyone think this could potentially be a long-term problem?

Here is a screenshot of each slot:

 

[CepheiA]

You shouldnt mix-and-match ram, it causes system instability.

http://www.tomshardware.com/answers/id-1702500/mixing-ram-voltage-problem.html

 

[TheoSqua]

Would i be better off using the old 8GB stick, or should I stick with the faster 4GB for better compatibility?

 

[Tradesman1]

Yep, any time you mix DRAM it can be problematic, best just to get a set of the full amount you want, many will tell you to go ahead but they are still back in the ages of DDR and DDR2