Not a C1 versus RSP response here, but just on Magne Nilsen's profiles:
I've been using Magne's C1 profiles (D30,D60,20D) for some time and am not sure if the "film curve" was the one originally used to create the profiles or what since the "extra shadows" curve seems to give a more accurate response. My point being that with each release of C1, there seems to be subtle changes that affect these profiles a tiny bit. I queried Magne on his web site at about version 3.7.x something and he said that he wasn't aware there had been any changes, though.
With RSP and the color engine dll that bundles all the ETC profiles, the one for the 20D seems to be producing results between lo sat (my preference) and hi sat and the extra shadow curve in C1. In other words, you'd be hard-pressed to see any difference as far as color goes between the two. Which is a good thing!
Basically this is all from the perspective of the type of landscape photography I do.