I am going Valvoline HM synthetic on next oil change cause it was cheaper. I am not concerned although I have 17k on it but like hm oil especially Valvoline as it conditions the seals not swell them. On older formulas seals seem to harden over time so it could be a good thing. With the difference in 100C is minute but I would think lower number would flow better. Either one works as both are 30 grade.