H100 is the best performing, but can be noisy and a pain to fit. What sort of overclock you have in mind? Anything below 4.6GHz, and a SilverArrow / H100 / NH-D14 is overkill. H80 is decent but expensive, otherwise look up £30-£40 coolers for those high / midrange clocks. True Black, Venomous, Megahalem, with various kinds of fans.
If you want to play around 5GHz, a SilverArrow, H100, or a full blown water setup.
Can't say about the 920, the H80 is quite popular.