The original Cayenne I bought at the time of launch only was available with steel suspension (Porsche keep the air for the Turbo at this time), to drive it was great, I would say as good as the air in sport mode but as a passenger and especially one in the rear it was bouncy and uncomfortable, only kept it for 6 months because of this and switched to the air. As for the air suspension all three are very good, the Q7 and the first air suspensioned Cayenne I owned were roughly on par with each other with the Porsche offering better steering and brake feel, but the new one is a definite step up from either of them, probably to do with the weight reduction as much as anything.
Off-road, in a Porsche? 
Well I have but just not in my own. I did do the off-road course at Porsche's driving centre at Silverstone but that was in the older model, haven't been invited over for a try in the new one but it's only a matter of time so will report on my findings at that time.
As for my preferred setting so for, normal with the ride height also at normal when driving on normal roads and motorways, on less than perfect roads (we call them B-roads) I perfer the comfort setting, it still offers decent body control but just smooths out the imperfections that bit better. One thing I am findings is that passengers complain it's a bit unsettled when you drop the ride height to it's lowest drivable setting (the one above loading), it does look the part but probably best left to motorway driving.
P.S.
The interior is as much as anything which swayed my decision, the past Cayenne was a joke, if you didn't order full leather then you lost big time come resale but it wasn't only the finish of the dash and door capping but the quality of the switchgear and air vent units that let the side down, thank heavens Porsche have addressed all these shortcomings and finally given the Cayenne an interior befitting the brand's status.