I guess what he really want to know is the lifetime difference between having it OC to 240 mhz and having it OC to 275, if anyone tried it and could answer that it will be great.
PS: an addition to the sticky is that GP2X wont run all the time overclocked, in other language, if someone bought a guranteed 275 mhz unit, the clock speed will vary in regard to the application used and the settings the users will choose, people here are able to use the MP3 player (fw 2.0, not sure if it is the same in fw 2.1) while they have their GP2Xs downclocked to 100 mhz only.