I actually added the Logout URI incorrectly. Support had advised me to add it as /owa/auth/logoff.aspx*, when it just needed to be added without the star. It now properly closes the APM session when logoff/signout is clicked in either OWA 2007 or 2010.
Still working on the OWA timeout issue. We have it mostly working, but we are getting very strange errors in LTM Logs when the timeout iRule processes: "http_process_state_header_xfer - Invalid action EV_SINK_HEADER during ST_HTTP_XFER_HEADERS"
Have a more detailed post here: https://devcentral.f5.com/Community/GroupDetails/tabid/1082223/aft/2163383/asg/62/Default.aspx
Nimbostratus