Modern FI cars won't ping because the ECU retards the timing to make up for the lesser punch of the lower grade fuel. But the leaner mixture is bad for your cylinder heads in the long term, the leaner combustion can cause cylinder blow-by and burnt heads. Stick with the 91 / 93. My 968 ended up losing a good deal of power when I moved to CA because it was designed to run on 93 octane minimum and the most you can get out here at standard pumps is 91.
As far as the 100 goes, I dunno, but 110 octane race fuel (VP for instance) has additives that help increase power on their own--the timing and whatnot doesn't need to be adjusted. That's why racebikes can use it when they have open-loop FI systems, the system doesn't need to recalibrate itself to the different fuel. I don't know if the 100 gets to 100 octane through this type of additives or if it's just really pure fuel. I suspect it's the former though. Can't hurt to try though--the worst that can happen is nothing.
