its a 285 cam, idles very lumpy (some love it, some don't, I...love it).
No idea on emissions, have not had the car tested for them, however, I have lost about 5-8 mpg through normal driving.
Gain wise, yes it is noticeable. Below 2700ish rpm it has lost power, but once it is over that the gain is very good. It used to run out of steam at 5500rpm, but now pulls all the way to the rev limiter.