I've not read anything good about the NISMO exhaust. 6 hp or something, what a waste.
I thought resonated test pipes was fairly close to HFCs but maybe not. The FI setup I heard had all the extra resonators but with test pipes and it didn't sound much quieter than mine, and it made my ears buzz with drone. I'd be interested to hear your setup if we ever hit a meet.
And, if it's too quiet, we can trade and you can have GTS again.