Shoes generally last a bit longer on clay...I play on har-tru and hard court in the summer and my hard courts eat through my Barricades and barely any noticeable wear on clay. Good luck, clay is great stuff to play on!
From my personal experience, Har-Tru is very forgiving on hard court shoes. However, once those shoes get some wear to the point a hole is forming, the sliding from clay courts will wear them through pretty quickly.
The sliding on the clay will wear your shoes out eventually, but it normally takes me about 6 months of playing several times a week until I notice my shoes getting slick and losing tread.