It may not be as fast as the Galaxy S series when it is overclocked, but the Samsung Nexus S can be stably overclocked at 1.4GHz. This is not too much less than the 1.6GHz of the Galaxy S series, but when we think about it is that much speed really necessary on a smartphone. Most of us whom own these sort of phones do not need this type of processor speed, but this always comes in handy if you ever do. Personally I find that even at 1GHz processor speeds it is more than enough to get the job done. Extra speed is always a good thing to have though so to go above what the phone should be running is enough to satisfy me.

Sources: Phandroid XDA Brief Mobile