History tells us, Moving down=BADDDDDD
Most of the weight an athlete loses is muscle mass! Sure if you weigh 300 and are 5'5" it might work but there is a reason fighters find a comfortable weight that doesn't drain them. Not only do you lose muscle but often you dehydrate, which is dangerous later in bouts!
Valuev will be a beast if he goes down to the flyweight division. :D
http://i100.photobucket.com/albums/m30/taga_ipil/brokegayweathers.jpg
http://i50.tinypic.com/20awjgy.jpg