I run Shell Rotella T SAE 30W. Getting hard to find though. My oil pressures are ~30 psi at 32-3600 and full operating temp with OAT of 90+ in Pensacola, FL.
I did my fall oil change before storing the boat for the winter and put the 15w40 rotella in it again. Oil I took out with about 50 hours on it looks perfect so I’ll keep you updated! Lol!
I use straight Rotella 40 wt in my 1998 31 open
Used straight 40, 1500 hours had top ends done. Switch to pure syn, 15/40
2100 hours going strong.