As I have the Thundercat donor bike I'd wondered about the ram air system being transfered to the fazer but my skills lack for that much, as far as I can tell it would require changing the carbs too, and I'm not sure if that would mean also swapping ecu's, as there's a lot of questions and all my work is done out on the road I don't think It's feasible for me, especially as the maximum time I'd have to play would be a weekend as I'd need it running for work!
People should stop thinking the bikes share this and share that, they don't, there's probably a handful of things at most.
The extra power of the cat is definitely noticeable, the ram air system isn't just a tube straight into the air box, there's 2 extra (smaller) air boxes in either fairing which the front scoops feed first then it goes into the airbox, obviously the size and shape of these side air boxes do some wizardry to the air flow and possibly density!
I do prefer the cat, just for the extra bit of power and its just as comfortable to me as the fazer!