Just wanted to throw my 2cents worth in here. I received mine today and they look great. Heres the thing, if you want the max gain in hp it looks like the stillen's are the way to go (although im still not sold on some of the dyno results). The reason to purchase any other is for the ease of install and also to maintain, plus the look and sound change. These were purchased solely for the look and sound, whatever hp gain there could be is just a bonus. I didn't want chrome like the "T"'s have and the JWT still use the stock plastic elbow. So these looked like the best way to go. So if your concerned with hp gains you know what to do, if not then go with what nissan would choose, NISMO!
Oh one last thing, the Nismo got around +10 on the 350Z