Just a couple of thoughts from my Turbo 958 experience . . .
You needn't worry in the least about the CTT having too much power, since if you are not trying to make it wail, it's totally a pussycat. The transmission likes to quickly get you into the most economical gear possible, so a lot of your time is spent plodding around in seventh or eighth as docile as can be. Press the throttle hard to get some boost and some downshifts and the situation changes dramatically, but that's entirely up to you. (It is, however, very handy to have the small 50-90 time that quickly and safely gets you past slow traffic on crowded two-lanes.)
The tire situation for Turbos is not good. There are serious body and component clearance issues, but the initial problem is that the smallest diameter wheel that will fit over the Turbo front brake disks is a 19 inch. And the number of suitable true all-terrain tires available in 19s is really small. I ran 255/55R19 DuraTracs and that tire--just a bit over 30" in diameter--was the best I could do. Goodyear has the Adventure All-Terrain in a 255/60R19 and I ran those, too; there were a little over 31 inches and were a wussier tire (which was good thing when on pavement) but the clearance with the front fender was too tight. So by the standards that have taken over herein, you might well eliminate a Turbo for the tire size problem. In reality, if you are on paved, dirt and gravel roads, 30 inch tires are plenty big and give much better handling, ride and fuel economy than shoehorning on bigger ones.
I've actually never analyzed how the front facias of Cayennes compare, but mine is equipped with the front and rear factory skid plates--cleverly bent aluminum pieces that, knowing Porsche engineering, may work better than you'd think they would . . . or maybe not

--and thus I have decent angles and clearances. I would guess that a non-air Cayenne on 22s is would be pretty suspect.
As often happens here, decisions have to be made between getting the apparently cooler, more trail-oriented truck and suffering the downsides when you are not on a trail or getting the less "built" rig and gaining advantages for the vast majority of the time that you are not trail running. I would propose that a properly-optioned Cayenne, whether diesel or turbo, ranks as a exceptionally good off-pavement truck, but it's probably not amenable to a hard-core trail build at any practical cost.