Originally Posted by xluben
What you're saying is basically true but there are some other things to consider. It's the distribution of the weight that really matters. If the CF shaft were large enough diameter, and hollow (all the weight at the perimeter) it could actually be harder to turn that a smaller, solid, heavier shaft. This would all depend on the actual weights and measurements though. In general the CF shaft would almost always end up being easier to turn.
The distribution of weight basically is the polar moment of inertia, and the aluminum shafts are hollow, just like the CF. The aluminum ones are often bigger that the CF ones just for the sake of torsional stiffness, since aluminum has only 1/3rd the stiffness of steel.
I have no idea how much the inertia difference really translates into real-world difference, but on paper, in concept, it certainly begs one to look at more than just the weight.
To be honest, I'm really most interested in any one-piece DS just for the sake of ditching the two-piece design that bucks like crazy sometimes. I'd say your car definitely deserves a CF DS.