I think that's a bit much to ask an AppleScript to do. You can probably do it better (and faster) manually. Additionally, testing such a thing would require me to create duplicate tracks at different sizes, times, bit rates and what not. I'm sure you'll agree that doesn't make much sense for me to do : )
However, if someone else wants to modify the script, be my guest.
To add shortcuts to AppleScripts in the iTunes Scripts Menu, read this