Las Vegas - oil weight to use?

[Haxir]

I think I posted about this a few years ago. But I've since read other information about what weight of oil to use. Last I posted, people told me to use 10w40 in the summer months here in vegas, and back to 5w30 the rest of the year. But I had reas 5w30 covers up to about 120F? Should I use the 10w40 due to the heat and Turbo?

I use Royal Purple btw