OK, back from our trip a couple weeks ago. All went pretty much according to plan. We arrive in Tarbes (by train) late Saturdayand miraculously, there was a cab waiting that was exactly big enough for the two of us plus our bikes & luggage. It required some ingenuity on the cab driver's part to rearrange the interior of his car, but he happily did so. So that took care of the 4 miles from the train station to our hotel.
The next day (Sunday) we had a pretty narrow window that we could pick up the car, at the Pau Airport. My guess is that they coordinate their hours for when the planes arrive. We rode our bikes the 35 miles and arrived with maybe 20 minutes to spare. Ended up with a Peugeot 207 which was going to be a bit too small for our bikes & luggage, but it was a very easy car to drive.
I did go back to the rental counter with a question before we left, but they were gone. Not just Europcar, but everyone in the rental row. In fact, the entire building was locked up! If we'd messed up our timing, we would have had to wait another 3 hours.
Regarding the small size of the Peugeot 207, we were able to deal with the bikes by buying a bike rack at the local Intersport in Tarbes (65 euros, which seemed like quite a bit, but probably less than the difference in price if we had been able to go for a larger car).
Returning the car to Cognac wouldn't have been difficult were it not for the final time trial stage of the Tour de France ending nearby!
The moral to the story? When renting a car anywhere but the very largest cities in France, you may have to plan things around the car rental, which can give you the impression that everything's going to be a hassle. But that's not really the case, and try not to let it wreck your vacation. It's part of the adventure! And remember, if you expect everything to be the same when you travel for fun, why, exactly, are you traveling in the first place?