I believe a paid F fare would have priority over e500 upgrades. However, by flight time most F upgrades available might have been filled.

I don't think PPro get free Same-Day confirmed.

Personally I would take the chance on sitting in an airport for 4 hours, in return for a chance to get a lie-flat on a long-haul flight and to get to my vacation destination 4 hours earlier.

I'd start by going to the ticket counter when you arrive at the airport. If the flight is not oversold AND they have an available F seat, they may well confirm you then and there.

One small downside; if they cannot confirm you, you probably can't check in your luggage until 4 hours before your scheduled departure, so you may end up waiting at the ticket counter (if you are checking a bag) for a while. You'll obviously have to get there at least an hour or more before the earlier flight, which will be 5+ hours before the departure of your scheduled flight.