Rotella T6 -> 5w40 vs 15w40?

[GoldOxide_imp]

If I lived and rode in Texas during the warm seasons, I would consider 15W40 and experience and understand its performance on the bike. 5W40 is useful during winter and summer riding in southern Ontario.

Air cooled V-twin riders often use 15W40 even in the northern regions of North America.

Many Moto Guzzi riders use 10W60, as per the manufacturer's recommendation.