I've run M1 in all my cars for over 20 years and the biggest benefit is obviously the change intervals but with any hard driven vehicle synthetics maintain a better temperature consistency and resists burning or "coking" (on a turbo application) and still flows nicely at sub zero temps at engine start up. I've never noticed a different from my butt-o-meter but it's peace of mind that makes me feel better.
'12 Focus Red Candy SE Sport 5 spd
'99 Toyota 4Runner Sport
'11 Subaru WRX STI Hatch