If you want to do a light overlock I suggest the Cooler Master 212 Evo, but you also have to remember that you might have a bad cpu ( in the sense that you might need high voltages to achieve a certain overlock, high voltage = more heat and higher temps) now it all depends on your budget! if you want to go crazy you could buy the 212 Evo and save for a year then you could create your own Custom loop, but thats if you want! If you going AIO I suggest the h105 (this is the one I have and its does a good job.) I don't really suggest 120mm AIO because for a good one you usually pay around the same price as a 240mm.
any other questions just let me know!