I did this 997 last month, and the paint was so soft, I had to do several test spots before finding something that wouldn't leave buffer trails, or micromarring. It was in pretty good shape to start with, Bryan "gmblack3a" corrected it last year, so it only had light wash induced swirling and marring. I ended up using UltraFina with the Flex, and a blue CCS pad, at speed 5. That worked like a charm. I even did an alcohol wipedown, and let the car sit in the sun for a few minutes to double check...
Now, on that same car, the bumpers were in horrible shape. When Bryan corrected it last year in Atlanta, he spent 12 hours on it, and ran out of time before the client had to drive back to Charlotte, so he didn't get to finish the bumpers. The bumpers were rock hard, from the flex agent Porsche added in to the paint. On the bumpers, I tried everything from Presta 1500 with wool on the rotary, to UltraFina on the rotary, and what was happening, was buffer marks were being left on the bumpers, but no correction was taking place. I ended up having to use SIP, on a white polishing pad with the Flex. With this combo, I was able to put a lot of pressure on the Flex, and really work the SIP without the bumpers heating up as quickly as they would with a rotary. I then followed with a second round of SIP with the Flex, with no pressure, and then finished with Ultrafina on the Flex.
The metal panels on this car, and the plastic panels definitely responded oppositely.
By the way, here is the same car when Bryan worked on it last year...
http://www.autopia.org/forum/click-brag/99265-2007-black-porsche-carrera-s.html