Okay, first off, I own a 07 Civic Si. I never said the r18 is stronger than the Si, I only said that turbo is more suitable for the r18.
Supercharging the r20, in my opinion, is a much better option for the si, only because it can only handle so much psi ( again, due to vtec). You'll blow your engine if you have too much pressure with turbo ( and also superchargers, but it's much safer with superchargers).
There's a reason why evos and imprezas can handle 20+ psi and our engines can't. Do not get me wrong, I love my car and engine in every way, but I am no bias to only my 07 Civic Si sedan.
I have spent a year debating on whether I should go turbo or sc, so don't think that I haven't done research on this. Turbo is doable on a r20, yes, I have never denied that.