How safe is it to 'mix' RAM?

Solution 1:

So as Kevlar said above, It shouldn't be a problem too mix the RAM up but you should still check that the voltage is the same otherwise your laptop will not boot-up.

Your other question regarding the CAS Latency:

Download CPU-Z from here: CPU-Z v1.65

CPU-Z is a free tool. With CPU-Z you can find out CPU-Name, Codename, Technology Core Speed, Multiplier etc. And you can check what your CAS Latency is.

Looks like this: (CPUID Homepage: CPUID)

Solution 2:

in most modern machines mixing RAM is generally OK. at least I have never had any issues. But it should be noted that RAM will run at the speed of the lowest module.

So placing 2x8GB in the back slots along with the 2x2GB will not give you the power you might expect. Even though more ram generally means vroom vroom!

4x4GB would be a better option IMO. or Just 2x8GB and remove the 2GB ones completely