I'm in Canada and temperature is about 15c, I have a water cooled wet sump Kawasaki 800, I put in Rotella T4 15w40, I'm always concerned about start up engine wear, should I be using T6 5w40?
Of the many things I spend time thinking about in regards to maintaining and riding motorcycles, startup wear falls exactly nowhere on the list. But that's just me.
Put it another way - I'd bet money that most of the wear on still-running high mileage engines is not due to startup wear.
It's a motorcycle - things wear out if you ride it enough.
If you really believe a lower W grade reduces startup wear, why not run a 0W-40?