Technically any RAM over 1333MHz/1600MHz is overclocked, hence the (o.c).
To be honest, most games at the moment don't take advantage of more than 8gb of RAM. 16gb would be plenty.
I use the TeamGroup Vulcan 2133MHz modules and they behave brilliantly. They also have a lifetime warranty with OCUK which is good.
I'll admit I've got 32gb installed at the moment, but only because I work with 3D design and that does need more than 16gb when running detailed stress analysis simulations.
P.S. What processor are you using?