I got a little better than 4000 miles out of my last two BT56's. Thats letting them go into the wear bars a little. I don't think I baby them, but, I also dont spin 'em (much).
My next set is going to be the Avon ST 45/46. I have heard some good things about them.
The stock front made it (just) through the two rears so that has better than 8000 miles on it.