I think we should add a step 6.5 (before step 7 Stop both servers) with something like:
If you are upgrading both a primary and standby, then we need to make sure the standby is caught up.
If you are wal shipping then on primary run: select pg_switch_xlog();
shut down primary
before you shut down the standby make sure it gets caught up to the primary.
I don't think its 100% required for them to be exact, is it? If they are a little different then rsync has more data to xfer from primary to standby ... but it would still work. Right?
-Andy