Hi all,

just found this on my travels through the Internet, thought it might help somebody:

How to Compress xlsx Files to the Smallest Possible Size » Bacon Bits:

The basic principle is that an xlsx file is actually a zip file, but Excel doesn't do a very good job of compressing it so you can squash it by zipping it yourself

Using this method myself and 7-Zip I shrunk a file from approx 60mb down to roughly 42mb, but YMMV