You'll be well served by H40, H55, H60 or H80i then. All of those will cope admirably with a 4.2 overclock when used as an exhaust. Get the H80i if you don't have a fan controller so that you can tweak the fan speeds as you please.
The H40 has an aluminium cold plate, you are better served by a copper one. I found this, it doesn't have all the models but it is shows some of them clearly:
Your looking at a degree or two at most with the copper plate. If your not pushing high voltage then save the money for something else. Its more than capable