i need to change my oil and i have been using the penzoil sythetic 5w-30. i was wondering if that oil is any good or not and if i should still stick w/ the 5w-30 or go to 10w-30. my car has 50,000 miles on it. I was thinking about switching over to mobil1 supersyn 5w-30, but wasn't sure if it was worth the extra money over the penzoil synthetic. Would the mobil1 oil be better than the penzoil one? and if so, mobil1 makes different formulas of oils, would the supersyn formula be the one to get instead of the others? thanks.