its barely better than a stock cooler mate. although it will cope with fast temperature fluctuation better than an air cooler its not really designed for over clocking.
the fan that ships with it only pushes 57cfm, the radiator itself doesnt have a very big surface area so while it will handle the cpu temps well enough there wont be much in the way of headroom for overclocking.
yes it will get you to 4.2 but you will be very close to your max temps at 100% cpu usage.