I have always heard that the low number is the important one. I use Motorcraft filters and have never had a problem. I also use Motorcraft synthetic blend oil. Good bang for the buck. I have used Mobil one 5-20 in the past and the motor did seem to be a little smoother. Other than that I did not notice any other difference. I still got the same gas milage and the power felt the same. (So if it is for free, it is for me) that what I say.