I was going to use a synthetic this winter here in Minnesota mainly to get better cranking @-20f or so. The last winters i could crank very slowly at -20f with a 650cca battery and Havoline 5w-30. Well, my battery died and i bought a 950cca battery. This should be a stronger battery at -20f than my old 650cca - right? So i should be ok with Havolione 5w-30 and not have to go with synthetic - right? Any comments or thoughts?