I have a 256 and 257 and I use a 13" MBP in a thick sleeve. The 13" MBP fits the same (very snug) in the side compartments in either bag (same width). However, it does fit more loosely in the center "pocket" in my 257. I think a 15" MBP would fit in the center pocket of the 257 by itself or in a thin sleeve.
6/4/13 at 6:45am