I'd be concerned about the winter weight. I see snow in your avatar. My worry would be sufficient lubrication in the mornings with temps in the teens (?).
It's a hard call, I've done this project and it's kinda expensive (four quarts of 75W-140 Mobil 1 cost $62). Plus, it's a bit messy (not as bad as the tranny drop 'n' drain, but still nothing to sneeze at).