No, Paris is in both the northern and eastern hemispheres. Locations in the Southern Hemisphere are south of the equator.
Without trying to sound patronizing, it's going to depend on your airline's schedule. A direct flight would easily take 11 hours or more, but many flights have stopovers and hub connections that would make the trip longer.
One of the best ways I've found to research flight times is to go to one of the main travel websites such as Orbitz, Travelocity, Expedia, etc. and use their flight planning tools to create a sample itinerary. You don't have to actually book the flight, of course - just cancel out of the session as soon as you find the information you want.
AVIS has offices at London Waterloo, Ashford International, Lille Europe and Paris Gare du Nord. I don't think any other company has all four, but you can certainly drop off an Avis car at any Eurostar station.
Portland, OR (PDX) to Paris (PAR) Shortest Flight Duration * 12 hours 25 mins * Via Frankfurt International Apt, Frankfurt (FRA) * this includes transfer time at Frankfurt International Apt, Frankfurt (FRA)
it will take 15 hours from LA to Paris