If you run synthetic IMO you'll be fine. The lower number is for cold starts, higher for better protection (viscosity) under load hot. Best to really ask a pro builder.
What are you worried about fuel economy? LOL
Newer vehicles have gone to lower viscosity for fuel economy and tighter tolerances is the way I understand it. Foe example most cars today call for 10w (or less) 30. IMO it's mostly for fuel economy and they can run lighter oil for tighter (longevity) tolerances in the engines.
But What Do I Know!
