Anyone have any experience with Grand Bois tires?

I have a set of 25 Conti Grand Prix 4 season tires, but after reading this thread I'm thinking of going with 28s. The 28 is as large as my bike will take. Not sure of the difference between 25 and 28. I've test rode a bike with 32s and they were nice.

I'm not overly concerned about tire weight, but I do have several long hills so it is a consideration.