First congrats on you JAN build, we all remember waiting for our Cayennes and sometimes the anticipation is too much!!!
The reason I chose the 20" Sport Techno's initially was mainly due to its AWESOME look. I had the Cayenne s 18" wheel on before and the 20" substantially changed the look of the car - much more aggresive. I know that people don't think that weight discrepancies matter on the Cayenne but I felt that the Sport's were a bit heavy (they wiegh about 65 pounds each with tired on and the 28's weight about 62 so thats 12 pounds difference in unsprund weight) I had just switched to BMC filters before installin the Sports and was enjoying the low end grunt, but installing them restored the cars performace to pre-BMC. Maybe I am just being too sensitive about it but I think this to be true. I think the handling and performance are about the same. You do feel more bumps in but I think they corber much better. I have not yet taken them offroad, but I feel I live at the top of an ant hill; there are so many bumps and I have gone over 3 or 4 curbs with the Cayenne and the air suspension handles the situation marvelous with both wheels. Anyways this is getting long - we are here to share not blabber.