As I've only done a 120 mile run on the new GSA I'm not really able to comment other than so far I think the Adv seat is more comfortable than the standard GS one.
Perhaps I've also got an oddly shaped posterior, possibly scupted by 10+ years of riding KTM enduro bikes - I once did the National Rally on a KTM 400 SC, complete with enduro tyres, (900+ miles in 24hrs), even got my picture in the BMF mag for that painful experiment. Not being one to learn a lesson easily I also rode a different KTM 400 SC in a week long RoD (Rally of Discovery) in Ireland, one of the days was 300+ miles in 8 hours. After those ANY "normal" motorcycle seat is comfortable.