It is all about flow anyway. High flow is preferable, to keep
oil moving across all surfaces.
If you want high pressure......you are not getting flow.
Elmariachi lives in Texas. Hot Hot Hot so start-up with a 40 weight is no problem.
It is a fact that you get more real
oil out of a straight weight than a multi, because of all the additives in a multi weight. So in this scenario 40 weight is most likely perfect for him.
What pressure are you getting now?