Retina iMac ram upgrade: voltages and timing

Hey people! I'm in the process of searching for RAM upgrades for my retina iMac. I'm in a bit of a pickle however. It is really hard to find suitable RAM here in Hungary and international shipping is out of the question sadly.

Anyways there two kinds of ram that I found suitable. The first one has the correct timing (CL11 if I'm not mistaken) but they run at a slightly higher voltage, 1.5v instead of 1.35v. The second kind one has the correct voltages but different timings, some are CL10 or CL9.

Now my question is: Will it harm my Mac if I put in a RAM that either runs at a higher voltage or has slightly different timing, but both are from reliable manufacturers.

Thanks in advance!
Cheers!

Szabolcs

Edit: This just popped into my mind after reading some other threads. From what I've read, iMac rams usually run at 1600Mhz. What about installing a ram with a higher frequency?