All of my biggest carpet python's sheds seem to not roll out nicely, and end up being about 3/4 as long as him due to a wrinkle factor.
Our rainbow boas however shed EXTREMELY nicely, and in fact don't even roll up their sheds. Their sheds come out completely straight off of their bodies. Next time they shed I hope I'll remember this thread so I can measure and come back with results.
For fairly accurate length measurements, use this program:
http://www.serpwidgets.com/Apps/measure.html
just take an OVERHEAD picture of your snake on the floor with little to no angle so you get a nice, flat 2D image without any depth of field. Make sure you have a ruler or extended measuring tape (or other measurable item for size reference) in the picture. The longer, the better and more accurate you will be. Use the program as instructed to measure your snake!