It actually depends on which 757 you're on.

The old 757-200 5500 series ("755") mostly have very small bins. Those are the 757's without any window exits.

The newer 757-200 5600 series ("756") and 757-300 ("753") have bigger bins. Both of those have window exits.

See:

http://www.flyertalk.com/forum/showthread.php?t=489160
http://www.flyertalk.com/forum/showthread.php?t=351347