I wouldn't try it....Windows 7/8 will give you the BSOD quite often...it would be unstable.
With the speed and sensitivity of today's CPU, mobo and RAM, it is unwise to even install RAM that isn't from the same manufacturer's run. I personally only buy a full kit to install in a PC - never mix them. An example would be if I wanted 16GB RAM, I would be a kit of 4 X 4GB or 2 X 8GB in one package.
Mixing frequencies can very well cause stability problems. Especially at high clock speeds. Buying it from a kit is not really necessary as long as all the specs (freq/size/voltage/density) match.
There should be no problem them.