Im not sure why people would shy away from Stillen cat back. Yes FI looks better IMO however if you plan on lowering your car, the FI system does not have the clearance that the Stillen catbacks do. Performance wise, i have yet to see the dyno of FI vs Stillen CBE on the same car, but my guess would be that it would come out fairly close in terms of HP gained.
If you would like to hear how mine sounds ill post the link to my you tube video.
YouTube - 370z stillen exhaust w/stock cats VS HFC + drive
Good luck with your decision, Stillen and FI are great setups, im sure there are more how ever these two have been proven to sound good and perform good as well.
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Stillen CBE, Gen 3's and Berk HFC