I'm close to your latitude and run the 20W50 VR1. But given our temperatures in Texas, you'd probably be fine with the straight 40 as well.
Previous: 1993 Prostar 205
Red 1998 Closed Bow Ski Boat, PCM GT40, 310 hp, Standard Gear Reduction, Acme 4 blade, Perfect Pass SG/Zbox.
Tyler Ski Club
Be kind. Have fun.