Just a couple of comments.
-The 1/6th correction factor was again a rough 1st order approximation that I got from taking one quick look at one rotor picture and another one in a vertical cross section to see the vanes. The vanes in typical cast iron systems are clearly different than the ones in the pdf you posted and for them my 1/6th approximation is better. As you note is does not affect the comparison if both rotors are roughly the same which is very likely. I did not choose this number to bias either system. I did so because I knew the OD, a rough ID and weight differences. This value seemed to work fine based on my quick examination and the quoted weight differences.
-My figures above stand of how much thickness or diameter you would need with the 800 J/kgK material in comparison to the 13.8" OD iron Porsche rotors. An equivalent sized rotor of this material is at a SIGNIFICANT thermal disadvantage hence the much larger sizes required.
-In terms of the comparison of the larger CSiC rotor to the smaller iron one the results are obviously skewed in the direction favoring the CSiC.
The advantage here is from the larger rotor more than from the material! Also, I would say the figures are close enough that conductivity may just start to to be the deciding factor. We know the CSiC materials have a lower thermal conductivity so they will exhibit a larger core to surface delta T than iron. We need an estimate of the difference in peak surface vs. core temperature for two different values of conductivity (again FEM would be good to get a reasonable estimate of this).
-I also found some data that says in general grey cast iron, despite the type or alloy, looses considerable strength above 500 °C (and looses it rapidly with increasing temperature, source here: http://www.sae.org/events/bce/tutorial-ihm.pdf ). What this means is that yout Tinitial is likely way too high and in practice would be almost impossible to obtain on any real iron braking system under any conditions except the most deliberate fade inducing ones. A more reasonable value would be 500 as a max allowable.
-All of our analyses point to a larger peak and operating temperature for the CSiC rotor system. Hence having a T initial that is equal for both, given an equivalent near term braking history, is quite a poor assumption. I made that one too in my analysis, but I was considering a braking event beginning with brakes at the temperature of the environment.
-Nonetheless, assuming all of your other numbers are correct (didn't check them in detail), and again ignoring conductivity, it does under these circumstance show a slight advantage for the CSiC system. Of course, as you mentioned, it also ASSUMES you have an appropriately matched pad (which they didn't back them).
I think both of our analyses together shows the important conclusion.
CSiC systems are not hands down better. If you run an oversize system with the absolute latest greatest CSiC material and a carefully matched pad, you
may just barely outperform a cast iron system from a thermal perspective. But you will clearly out perform it on the weight side which is very important in other regards. More or less my point all along! Finally when you factor in cost, I would say you are actually taking a step backwards.