We are using Schwalbe Marathon Plus tires on our tour and have had nothing but great experiences with them so far. We've now come nearly 7500 miles and have only gone through two tires on the three bikes. In short, we are pleased beyond all expectations.
I can't beleive that you have worn out these tires at 7500 miles. I have a set on my touring bike that have at least twice that distance of loaded touring on them and I'm not even thinking of replacing them yet.
Happy Touring!