I have a place in western MA and do Greylock regularly. It has been closed for 2 years for the road reconstruction but my understanding is it is now complete. It's always been a great ride but improved road conditions should make it spectacular. My loop takes me up the backside (from the North) of the mountain, which is a bit steeper but was such an awful descent due to frost heaves and potholes that I preferred the somewhat less intense descent of the southern route.
I think a 39x25 would be tough unless you're in really good shape. There are some sections that are hairpin and extremely steep and come on the heels of a few miles of steady tough climbing. It's nice to have something to drop into so that you don't come to a screeching halt and tip over!
I hope to see you all up there this summer- the view is fantastic.
