Regarding the supported RAM speed, the processor will support up to 1333 MHz,
You can install higher RAM as long as it is not above 1.5 Volts, but the RAM speed will be downgraded to 1333 MHz, since the processor does not support above that speed.
So personally I would say that there is no point of installing higher speed RAM since it will end running at 1333 MHz.
Regarding the processor over-clocking, please check this comparison chart:
It shows that the 2700K can run up to 3.9 GHz and the 2600K can run up to 3.8 GHz with turbo boos. So the processor will be running find in over-clocking up to 3.8 and 3.9 respectively.
But currently we do not recommend over-clocking above that speed, any speed above that will void the warranty of the processor since it will be running out of specifications and we cannot guarantee any stability.