Cool app: diffopc
Reading the msdn xps forum, I stumbled upon a very cool app for those who are messing around with xps files: diffopc
With that tool you can diff two 'opc' documents, as xps follows this opc spec, it can be used to diff xps docs.
I tried it, and it generates a nice html report with the differences in the file listing, and it even generates separate html pages with diffs in case the part is not binary.
If you are programming xps applications, this is a helpful tool. Very nice!