Richard,
If you want to move from 08.11.09.129 to 08.11.11.123 you should be doing the recommended upgrade procedure.
However if you want to move from 08.11.11.111 to 08.11.11.123 it can be done normal un-install and install process. Even with the uninstall and install sequence, it would be good to follow the sequence as mentioned in the OPMS_Setup.pdf document available with OP Administrator installation.
There were few minor enhancements for multi-project environment in the 08.11.11.123 build.
Hope this helps.