I used to use 10 in the summer, and 5 in the winter.

They are easier to find than the 0W30 that my local Isuzu techs recommended to me.

I wouldn't worry about the Mobil 1 making it over 5000 miles, I'd worry about the motor. If you don't notice any consumption, and if you drive under normal circumstances, 5000 miles should be a piece of cake.