Let me explain a bit in more detail.
I live in AZ and used to use Castrol 20-50 in everything including my 80's Honda XR.
My Magnum motor is machined for a thinner synthetic so I run Castrol Syntec 5-30.
This is how I decide on an oil for any motor.
First obviously decide on a good brand. (Castrol and Valvoline are two of the best conventional oils I have ever used that are comparably inexpensive and readily available anywhere)
I note my maximum cold start oil pressure and the weight I decide on is the one that is just under that cold pressure when out on the road running at hiway speeds.
This means the oil pump is supplying every bit of volume it can without bypassing any.
Oil volume is just as important or more so than pressure, because flow volume cools the parts it runs over, and the more that flows over the parts the better it will cool those parts.
This is why we don't just throw 90wt in everything to get maximum oil pressure.
I might have said 10-30 in the winter and 20-50 in the summer, but opted for a good year round weight for use in conditions very like where I am. (cept for the humidity)
Using the same method with my Magnum motor I have 60lbs cold maximum.
Out on the hiway at full temperature the oil pressure is 55 lbs.
(this tells me I am flowing as much oil over the bearings as the pump can pump, and as hi a viscosity as it can take without bypassing any.)