What kind of tire mileage are you getting?

[Dave S.]

I'm going to be buying new tires in the spring and am interested in what kind of mileage you are getting from your performance or all season tires. I want something that performs well in the summer, but at least lasts for 12000-15000 miles.
I often drive at high elevation in the mountains of Colorado and while I don't drive it in the winter months it is not uncommon to see temps in the 30's and 40's even during the summer. I have noticed several people talk about bad handling of summer tires below 40 degrees or so, not sure if that's enough of an issue to be concerend with.

Recommendations???