I Have a full xforce 3.5inch turbo back on my R32gtr, for 2years now it has been flawless, it also gives out a wonderful RB26 note very deep tough sound. I have the xforce metal cat and make 362rwkw and I don't have any of these issues others are talking about.I tried a decat ran it up on the dyno and only lost 3kw. I did this out of curiosity back then as I to wanted to see the flow restriction I thought it would have.
Well hardly any and with this power my Garrett turbo -9s became the restriction not my exhaust. So honestly i say they are great and don't believe everything you here.
Cheers,
Dave