XDA Dev overclockers have successfully revved the Samsung Hummingbird's processor to 1.2GHz, with (theoretical) stable speeds of up to 1.6GHz expected in future kernel iterations.
"We now have a successfully compiled kernel for the Captivate that overclocks the phone to 1.2 GHz," XDA Dev member BlackJackboy confirmed in a forum post.
"[Yes], many are complaining about garbled audio on custom kernels, even compiling directly from source. [But] either way, that is now fixed."
According to BlackJackboy, the Hummingbird processor inside all Galaxy S models can theoretically be overclocked to a stable 1.6 GHz - and potentially past.
"[So], if a genius can do that...Please, devs, post a link compiled kernel so that I can put it in the OP and people can start hacking their phones, I'll give full credit."
BlackJackboy also asked other hackers and modders to help compile a boot.img that would allow easy kernel flashing via recovery mode.
"I have no idea how, [but] we would really be grateful, for all of us with either Linux or Mac," he added.