Big pack eh? It is due to leaving the 14,000' camp on the Butt with 6 days of supplies for the ridge and 2 days for going down the rib and getting to the Cassin.
Downclimbing the West Rib is pretty straight forward. It is quite easy actually just very long and since the conditions were rather icy it required a lot of face in front pointing. If there were more snow it would go very easily. Nice thing about the rib is there is good camping in several locations.