I have been wearing the Brooks Ghost 11s for a few months and have about 600 miles on them (that is a generous estimate, probably more). I typically run on grass/ dirt trails with the occasional run on concrete maybe once every two weeks. Yesterday on my 10 mile run I was doing some pickups in the middle and by the end of it had gotten 2 blisters on my feet. Never got blisters wearing these shoes before, is it time to buy new ones? Pegasus 35s?