I just went through the purchasing process and drove both: 4.8is & '06 CS. Here is the difference from my POV. The 4.8is is faster and outhandles the CS. Feels like it's built with better quality materials IMO. The CS has a more plush ride and a bit quieter in the cabin. For me it was an easy decision after driving the 4.8is. Acceleration is scary for such a heavy vehicle. The tq off the start is something to experience.....and the exhaust as mentioned before is perfect!

pyiu,
all 4.8is come with the pano roof (standard equipment)

 

I hava a 04 x5 4.8 and am looking for a replacement, went to Porsche and test drove a 05 ctt with the power upgrade kit and was impressed with the brute power but the cornering and overall feel was not that of a sports car
as is the BMW and we passed on the upgrade. I am still waiting to test a 08 ctt they have an option to eliminate body roll. about 6500.00 extra.

 

I've had owned the BMW powered Range Rover, the 4.6is and now the Cayenne Turbo. Must agree with everyone that though the CTT may be quicker in a straight line the 4.6is did feel a lot more sporty. Steering feedback was out of this world. Still I do not regret getting the Cayenne. Wifey loves it, and I love seeing her driving Porsches

-TTRon