Owners manual on oil viscosity. mechanical engineers trump oil engineers.
if in doubt, call the dealership on revised oil viscosity. ;-)
You could try half a can of gumout multi engine treatment in the oil. do not over fill your oil.
It comes in a metal can that looks like seafoam and is stronger than seafoam.
When oil gets dirty. which will probably happen quickly. change it. say 500 miles or so...
All you can do is try to clean it up inside really.. rings, oil wipers and ring lands.
vacuum drops dramatically at any "even slightly higher" rpm's unless it's being pulled out "in front of" the intake...
and remember no oil is good beyond 5-8k because of acid build up.
I like castrol edge. try edge hm. It has alot of boron and will really clean your engine up.
Sounds like a good engine !! good luck, man.