A_Harman, that Redline 15w50 sounds perfect. Do you think its better than 5w50?
As a general rule, wide multigrade oils like 5W-50 employ viscosity index improvers to achieve the qualities of each oil at the rated temperatures. Motorcyclists with shared sump eng/trans, who use 5W-50, 10W-60 (and similar) find that they shear very rapidly. Often lasting less than 1000 miles.
M1 15W-50 is very shear resistant, by design with a minimum HTHS of 4.5 (although tests at 5.1) .