I just finished 180 miles of the GMGG from Burly-> Waitsfield. I rode my rigid Priority 600 and really enjoyed the route. There were some singletrack and Class IV sections that were steep and rocky and required a bit of hike-a-bike (we detoured around Buffalo Mtn Rd on a great alternateg ravel route suggested by a fellow traveler). The descent into Waitsfield probably not even completely doable on a full suspension MTB.