What oil weight is best for the 2.5l?

[Idaho Red Rocket 3]

I ran Mobil 1 10W-30 for the first oil change in my first Boxster with the 2.5 engine. It was summer time. As I learned more about the car I changed to the 10W-40. I think if you change it out when you reach 3,000 to 5,000 miles it "should" be OK. Now about brand. Many are convinced Mobil 1 isn't what it once was. Many now like Castrol Edge/Syntec and some other brands. With my second Boxster S I to have switched to the Castrol. I've actually used Castrol brand oils in my motorcycles for over 40 years. I think brand is mostly a choice that is personal and based on what gives you peace of mind. But 40 weight is necessary.