Old post, but Google search led me here and hopefully my insight may help others.
Training for my first marathon this year and increasing my weekly mileage to 40+ miles now. Not sure if it's that my legs are a bit more tired, but man, my Epic Reacts aren't feeling as fresh as they used to. The forefoot seems to feel a bit more harsh. The outsole seems to be the same it's always been, but I'm wondering if some of the cushioning's flattened out a bit. I've got about 440 miles on them now and do pretty much everything in them except track and some tempo/intervals. I usually race in them too (mostly 7+ mile races) 'cause they provide great cushion and at a size 13, they're lighter than most of the competitions more cushioned shoes.
Gonna hit up some stores soon for an A/B test to see if there's a noticeable difference.