I've read a lot of comments about 5w30 used instead of 10w30?

I live in Arizona. These are reasons I've used 10w30. My neighbor worked at the Ford proving grounds. Their petroleum engineer said he personally "... wouldn't use 5w anything in any vehicle he owned.".

I had my Hyundai serviced at local Hyundai here in NW AZ every 3000 mi. The manual states 5w30. The receipt read they used 10w30. They said Winter or summer thats what we use here.. Brand new car being serviced by the manufacturer they wouldn't use 5w in AZ

I change the oil at 5000 now using only OEM filters, but have switched to Mobil 1 high mileage 10w30. There's 90k on car. It has been totally dependable. It doesn't leak or burn a drop of oil. Never a warning light Combined it avg 28 mpg.

If I changed to 5w30 what benefits are possible? The next oil/filter change will take me into fall.

Thanks