Personally I am not very heavy [110 lbs.] so I tend to get a lot of miles out of my shoes. Between 800-1000. For me it’s feel. My shins are sensitive so I can feel when the shoe starts to break down to a point of being bad for me. So I say go by feel. I currently use AVIA shoes and find their cantilever plate system is very durable and comfortable. Actually the most comfortable I’ve ever tried. I highly recommend them. Check out their site for their running shoes.