I recently suggested this very idea on a different boxing forum, and some guy said that Byrd had 10% body fat weighing 210 lbs. I figured that he was just spewing out some nonsense since 10% body fat is very low even for athletes. I remember Bo Jackson having around 8%:

http://fauvecreations.com/pix/murgal...Bo-Jackson.jpg

In any case, if Byrd is motivated to go back down to cruiserweight I think he would be a serious force in the division. If Vassily Jirov could do it why not Chris Byrd?