The factory cartridge bearings on the Gipiemme Grecal Parade wheels on my last bike (a Cannondale CAAD8 R900) had about 15K miles on them when I sold the bike to a co-worker. He has put another few thousand miles on them, with the same bearings in place. They have been through torrential rains and flooded roads for several days at a clip over the years. How much more durability do you need?