If your worried about the sound then you should hear it in person not by sound clips. I have the Nismo catback and it sounds different than in a .wav file, especially when the engine is under load.

 

Very happy with my Stillen True Dual. Increase of torque and hp across the powerband. But then again I got my reflash a week after exhaust install and dynoed then. Love the sound too

 

Since stillen adds weight, it is not really within the criteria stated by the OP.

 

I always wondered why ppl get so bent outta shape about the extra weight. Its only 20-30lbs if Im correct (which means nothing in the grand scheme of things). I dont see how that could affect performance... Also it said in the OP that he was considering Stillen true dual

 

Its not just the exhaust. If hes really wanting to build a racer, and or concerned about weight savings, than 20-30 lbs can add up quick when combied with the spare, the tools, carps/mats, hatch, etc.

In my opinion you should ask yourself whats more important. The weight savings or the look/sound. If its the weight savings, than nothings going to beat a single can, even if you get it in stainless. So you need to decide whats more important. Me personally, I run a single can HKS Ti, and love it. Yes its loud as ****, yes it drones if I sit at 3k rpm going down the road. How often do you do that though? At high speeds I dont have the drone. The weight savings were insane also. Combined with my stripped interior, and soon the CF hatch, yet still adding the wieght of the roll bar, I still came out ahead in what I want. To me that makes it all worth it.

 

I'd love to hear these exhausts in person, but there are very few Z's here, let alone with aftermarket exhausts.

At this point, I'm pretty much set on the NISMO with the low weight, modest gains, and nice exotic note. My only concern is it becoming too restrictive with an intake, spacer, headers, and HFCs...

I haven't ruled out the new Injen Ti yet, still gathing info. From what I've gathered...
- Looks fantastic
- The included H-pipe will probably resolve the drone, and one supplier said it would improve low & mid range torque over the older version.
- The sound is decent on a clip from the old version (according to one witness, both versions sound the same). But, the NISMO seems to be a bit more exotic... IMHO. And without hearing it for myself, I'm concerned with how loud it may be... I like a presence, but not obnoxious, and something I can live with for a 4 hour drive.
- Weight, I can't find any specs yet.

So...

Price: Slightly Injen
Looks: Injen
Sound: NISMO
Performance:Unknown

 

Have had the Injen Ti for 2 weeks now and love it. Havent heard any drone yet, running it with UT test pipes and DC sports SS headers.

 

Why you don't consider the Greddy Evo II?....Im only read some good stuff about it and IMO have the best look! Just my 2cents