sell it and spend the money instead for a new iMac and with a bit luck you have money left over , new processors are expensive for the E8600 (would not fit a used processor)you are looking at about £250 , and fitting it is not as simple as in a pc as you nearly have to take the whole iMac apart and one mistake and you had a working iMac , you would not be the first who did a upgrade and destroyed some vital parts