You need to flash 4.2.x kernel so that your device runs according to rom. Kernels are like brains. They control how your device works. Si flash an appropriate 4.2.x kernel when you flash a 4.2 rom. And yes OC means overcloak. It basically is a process of increasing your processor speed more than usual. Lets say if your processor is 1ghz, you overcloak it to 1.2 ghz. OC may speed your device, but it also creates heating problem and battery drainage quick. Hit thanks if i helped.
Sent from my Canvas 2 working on stock jellybean 4.1.1