In reply to wbo:
I don't use one pair exclusively, but mix them up with other road and trail shoes. I've had the following :
Rapa Nui - 600 miles ( uppers ok, outsole gone )
Challenger 1 - 460 ( uppers burst, outsole pretty far gone )
Clifton 1 - 400 still going, uppers perfect, outsole pretty far gone, will aim for 500
Challenger 2 - only 70 miles
Clayton - only 10 miles