Motor Oil Viscosity Grades Explained in Layman's Terms
understand a little bit first. Then let the melee begin.
You can always check your owners manual. iirc, porsche often has a page about oils and recomended viscosities based on use and outside temp ranges. (at least in my 944 manual it does).
Recall that in a watercooled 911 (vs an aircooled 911) the purpose of oil is protection of metal. It is NOT also the "coolant" like in the aircooled cars. Your car has water jackets, radiators and a separate cooling system to keep the engine in its correct operating range.
Now, if you were in an aircooled 911, I'd recommend a "50" oil. Could be that at 100 degrees, 40 or 50 would be adequate protection.