Email, calendars and address books in a GW 8 PO can all be accessed without problem using a 7.x client. One regularly reported problem is with item views using the GW 7.0.1 client. The easy fix is to copy the ofviews\win from your GW 7 client install into the PO's ofviews directory being careful not to overwrite the newer GW 8 versions of the view files--only copy the missing files.
It appears that the GW 7 client can export calendars and address books from the GW 8 PO successfully. The only issue I've seen reported on exports is when a GW 8 client exports an address book for use by a GW 7 client. GW 8 uses UTF-8 character encoding while earlier GW clients use ANSI format. You can export .nab files in the GW 8 client using ANSI format to get around this issue.
