This may not be the exact UI feature in salesforce that you are looking for. But you could compare the two metadata files in eclipse. This would give you a fairly good idea about the differences between the page layouts. In eclipse
- Select both the page layouts files, using Ctrl for multiselect, on the left pane.
- Right click any of the selected and choose 'Compare With' --> 'Each Other'.
This would show a satisfactory comparison between the metadata of both the files. It is possible to understand the fields and their relative ordering differences. Hope this helps.