That rumor is crap. At low revs, my car is fine. Not one single problem with the Q45. Idles like a dream.
Now, The Garret GT30 has a 4 inch intake. Why in the hell would you want to come 4 inch off the GT30, then drop the size of the piping to 3 inch to a z32? Can anyone say "bottle neck"?
Since the internal diameter of q45 is about 90% of 4inch, you lose very little intake size, meaning you can keep a nice big 4inch size all the way through.
I bought a Q45 for $180, and it runs fine, no problems at all. Z32s are the same or much more.
Also, You'll be able to use the q45 for your 380rwkw project...lol