p is the performance line form Intel for the 1155 socket. No integrated video support, and better OC support.
H is the mainline setup. It allows the use of HD2000/HD3000 IPUs on the 1155 CPU.
that 3rd one is a company identifier of a H67 motherboard.
It is not possibe to boost performance with an OC that I know of. You can only push so much data at a given speed.