If I were you I would seriously consider water cooling, it has become far more main stream than it used to, the days of having to build a custom system from scratch with components from a scrap yard and pet shop are gone (unless you like that sort of thing

) but seriously though some of the new copper sinks offer c/w ratings similar to that off low end water cooling this doesn't takes case cooling into account as the case temp is likely to be higher with air cooling unless you have a silly case fan set up which means even with the same c/w rating an air cooled heatsink is likely to still give higher temps. Usually water cooling will only get you 50-100mhz but it's nit just the extra speed that make it worth while, it is quieter (unless you get a dodgy pump) and also will keep the chip cooler plus it's easy if in the future you decide to go for a peltier setup as well.