Hi George,
As I understand it, you focus on having an as pure as possible file to begin with. No problems here. However, considering that the files that come out of your camera have been processed by the in-camera software that translates the data from your sensor into a Raw file readable by a Raw converter, the camera software is a major factor in determining what you get out of the file at the end. Therefor, what you intend to obtain through tests with an as pure as possible default file will only work with real life out of camera images when the test is done based on images coming out of that particular camera. Thus, if you create a default method that works on sensor A, it does not mean that it works on images shot through sensor B, and I am not even considering lens variables here. That is why I recommended the creation of a as high as possible tiff file that excludes all of these variables, lens and sensor.
As far as I have seen, but I do not know everything, Raw Therapee is a pretty good program, for you can choose between a variety of algorithms for demosaicing,and, furthermore, it offers an infinity of options other Raw editors I know do not include. But, to be honest; Raw Theree, at least on my Windows platform is a pain in the a… It crashes frequently and because I try to sustain myself through my work, I have to produce, and, of course, crashing programs do not encounter my needs. This doesn’t mean your computer can’t necessarily handle the program though. I would say; try it, if you don’t already know it. Raw Therapee is Open Software (that’s probably why it crashes), so; it is free and easy to give it a try.
Whatever you discover, please let me know. I am as interested in the possible results as you are!
Cheers!