Well, I can speak only from my experience.
The Boxster S I had, had a leaking evaporator, so the AC didn’t work regardless, and when I fixed it, I obviusely re-foamed the flaps.
On my 99 box and 02 996, there was/is no foam coming out anymore. So the flaps are naked for sure. I do not see any difference with the AC between the 3 cars. They are all blowing cold. The heater is a different story.
With that said, I do not like penguins temperature in my car, although i leave in FL.
Since I have the Boxster S (with the fixed flaps) and the 996 both in my garage, it will be interesting to preform a comparison between the two, using an infra red thermometer directed to the center AC vent (as described in the shop manual).
Maybe I’ll do it next week when I get back from my road trip.