No question that the Cayenne is going to be more satisfying for a competent fabricator (you) than a bolt-on guy (me). If you have the skills to put together your own package, there's no limit to what the Cayenne can do . . .
From AutoBlog:
Last year, a pair of series-built Porsche Cayennes that were further modified by the customers who purchased them drove to victory in the 10,000km-long Transsyberia Rally. Spurred on by the success shown by those two cars, Porsche has built a small production run of at least twenty-six 2007 Cayenne S Transsyberia SUVs, all of which will compete in the 2007 rally. The full range of Porsche's techno-enhancements are in place, including Porsche Traction Management (PTM), Porsche Dynamic Chassis Control (PDDC), and Porsche Active Suspension Management (PASM). The PTM system is further enhanced by a transverse lock from the optional Offroad Technology Package available to regular customers, and the PDCC system is already set up with a Special Offroad Mode, which, when active, lets the Cayenne ford bodies of water up to 30" deep. A roof-mounted snorkel keeps that water from invading the intake manifold.
But as to your questions . . . (WARNING: Not an expert

)
As I understand it, the Advanced Offroad Technology Package with the rear differential lock was optional on all of the models: S, Turbo and plain (V6) Cayenne. The stock setup allowed only for center diff locking. However, I've looked at a dozen or so S and Turbo Cayennes and have yet to see one with the Advanced Off-Road Package (identifable by sill protectors and skidplates) and I think the option is very rare. A Autotrader.com search of all the Cayennes in the country failed to find one using "Off Road Technology" as a search term. And that's the only way to get the disconnecting sway bars. And, what's more, I think the newer generation (2008-2010) ORT Package doesn't have the swaybar disconnect.
I believe the 2-speed transfer case was the stock setup through 2010, when it went away, even as an option. Given the costs involved, most of my looking was at the 2004-2006, but I think I'm right on that.
It appears to me like Turbo/non-turbo doesn't enter into the ORT Package. It does, however, affect the adjustable air suspension issue, since all Turbos have it as standard while a much smaller proportion of Ss, and almost no V-6s, were optioned with it. (The GTS model, slotted between the S and the Turbo, has it more frequently, but as they're newer, they're also pretty pricey.)
My goal was to find an S with adjustable air, rook rack and tow package, and they were available, whereas an ORT Package model is real hard to find. And Desert Dan is right; you can look at a 2004-06 VW Touareg as well, since the Touareg V-8 is only very slightly different from the Cayenne S, and some of them came with adjustable air.
One last helpful hint: According to jmarkoa, a Cayenne owner with the ORT Package (and a factory rear spare tire carrier; uber-rare) who posted on 6speedonline.com, the sure way to tell an ORT Package-equipped 04-06 Cayenne is to look for this center console switch arrangement with the swaybar disconnect indicator:
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Good luck heading down this road.