I have been wearing the ProGrid Guide 3 shoe and was very happy with the fit and durability.  I was hesitant to try the 4 after other comments/reviews I read.  One month in, I can say that the fit is as comfortable as the 3, but I am not sure that this model will wear as well as the 3 due to the slight design change in the toe box -- more fabric.  I will have to update on the durability -- especially since I am going to be putting some good mileage on these shoes in the next couple of months.