Chapelcreek, we just did a transatlantic in Nov. and docked LeHavre 12/2. I booked a private tour guide Le Havre to Paris for the day. Driver picked us up 7:30 am and off to Paris we went. 2.5 hr. drive each way and traffic was very light as it was a Saturday. We arrived in Paris 10 am. I had arranged our itinerary w/ the tour guide so we were able to see all on our wish list. I bought tickets to Eiffel Tower online and we had an assigned time of 1 pm, most everything was already booked. Our guide factored in the Eiffel visit and dropped us off and picked us up. It is about 1.5 hr. from ascent to descent. It was very crowded so we had to wait for elevators, etc. You would not have time to have lunch nor would you have time to visit Louvre (we just did a drive by). Tour guide said that you would need sufficient time to even see Mona Lisa so we opted to skip Louvre.
I would not suggest that you go the private tour guide route because of your time limits. We did not depart Le Havre until 9 pm. You would have to leave Paris by 3 or 3:30 pm in order to be back on the ship no later than 6 pm for your sailaway. Not enough time to really see anything in Paris. I would suggest that you take the bus into Paris, go right to Eiffel Tower and go to the top, then see how much time you have left for anything else. I would also suggest you buy your tickets online in order to save time or you will be waiting in a line to buy your tickets. You could do the hop on bus and maybe see a few other sights. Lunch would not be possible with the time you have in Paris. At the most, you would only have about 4 hr. to see anything. The busses would probably not leave Le Havre until 8 am and you would get dropped off around 10:30 or 11.
I planned our trip very carefully so that we could see the most in the time we had. I am not sure that I would even attempt going to Paris if the ship was departing at 7 pm.
Unfortunately, timing is very important when you plan Paris. Good luck.
I almost think I would do Normandy instead of Paris w/ your time limits. I would be happy to answer any questions you have.