Superman's power level is over 9000, but not by much.
It would be an even fight until Goku went supersaiyan. Only way Supes could take anything farther is if he were either the old school overpowered Superman who could close a black hole with his bare hands, or if he were the fucking roided out omega superman or whateverthefuck it was called when he had the green lantern ring and lived IN the sun.