I recently drove a new Plus 4 around Paris and spent time in traffic jams and driving at low speeds. This was a real test but the car didn't get hot in the way you describe and performed beautifully.
To be on the safe side I would give the dealer a call.
There is not a massive difference in power over the older Plus 4 but it was still a spirited drive - when you could find an open road to put your foot down and the French police were not about!
