Wouldn't book the stop, even if it tripled my upgrade chance. Unless you need the extra PQM's or have a best friend flying on the ORD leg, I'd take the non-stop in a heartbeat. United dropped the SFO-CDG route for a few years, and it actually made the decision a little more difficult for me during that period (though I still opted for AF as a 1k with no skyteam status).