I have a 2008 Mercury Mariner V6 with 180k miles. It does short trips during the week and an 80 mile run on Saturday. For 80% of the changes I use Motorcraft 5w20 synthetic blend but every so often I'll use Castrol Edge Extended 5w20. Am I falling for the hype when I use Edge and wasting my money? Oil change time is at hand. No engine problems and I'll have to add a quart halfway between changes which are every 7k