I am planning to buy some Mobil1 for my first oil change, and was thinking I'd use 0w-20 synthetic as per all of the recommendations I've read on GH, but noticed that Wally also has 0w-40 synthetic, and wanted to get opinions on the downside (if any) of using the 0w-40.

I live in Arizona, which is known for its heat and my concern is that the 0w-20 won't protect as well in the summer heat as the 0w-40.

If I'm not mistaken the 0w-40 should be able to get to critical engine parts as easily as the 0w-20 during startup, but I'd like a weigh in from those in the know.

For reference, I'm not a very heavy driver, having only 3250 miles on my '07 Camhy since picking it up in Sept. '06. I will be sticking to a 5k oil change interval on the car.