IMO it depends on the rest of the motor.
If it's an older LA converted to roller I would say 10/40 or 20/50
A newer motor like a magnum then around 5-10/30 full synthetic.
I run 5-30 Castrol Syntec in my Magnum because it was machined for synthetic when it was made.
I like to run an oil viscosity that when at temp running down the road my oil pressure is around 5-10 lbs less than the cold start pressures.
This tells me I'm not letting oil bypass, and that I have a good amount of flow through things.
My thoughts on it are a little lower pressures at temp because of a thinner viscosity means the bearings are getting the best flow of oil through them.
I firmly believe flow volume is more important than pressure.