They were extremely slow and noisy
but also extremely comfortable and roomy for a small car
They had an air-cooled flat-twin of 602 cc and 22 bhp in 1961, 25 bhp since 1964. Top speed was 105 to 115 km/h, but it took a very long time to reach that. Roomy enough for 4 adults and their luggage and with the independant suspension on all four wheels and the front wheel drive the roadholding was as good (if not better) than most modern cars, so once you had reached speed, no need to slow down for cornering. At least as long as you're not afraid of the extreme leaning, as a result of the very soft suspension and very long wheel movements.
I once had the oppurtunity to drive an Ami 6 from the South of France to Holland (some 1600 kms/1000 miles) and I was really surprised of the comfortable ride...
Btw, about the De Pontac Coupé, I'm not so sure that it had a Panhard engine, though De Pontac did make a racecar with rear mounted Panhard engine, the barquette and the coupé had a RAF tuned 2CV engine of 500 cc. In the 90s I spoke to the French car journalist Dominique Pagneux, who told me that he had recovered teh remains of the flower-decorated De Pontac. But never heard anything ever since, so I guess it is still awaiting its restauration.
(picture from Automobilia #61, mars-avril 2003)