What you are proposing is in the arena of long distance trail running, where the ascents are walked and the descents are ran, with the flat areas done by a bit of both. Doable with a few years trainig, because it will take a few years of regular long runs and walks to build up any physical and mental stamina, never mind the amount needed for such an undertaking. I know it has been walked in 5 days on a number of occasions, which although a tall order, is within the capabilities of an experienced very fit fell/mountain walker.