Pc overclock help needed?

ive got a core 2 duo and its a 2.4ghz. ive overclocked it to 2.8ghz by putting the bus speed on max and voltages on my parts recomendations. if i up the voltages can i get it up to 3 ghz. or is there a better way to do it? also is the fsb ok at 140mhz over the processors number?