I work at a motorcycle shop, I hear quite a few come and go. Project SC is known to be one of the loudest. I like them on the Aprilia V-4's and that's about it. And I respectfully disagree, not all are equal after the cat is gone. The Termi doesn't equal the Projects. It's more of a raw, near obnoxious loud with them. Same with Toce, makes you wonder if there goal is 100% looks and zero fecks about sound level/quality.
You want quieter, get long and larger diameter. Both will help bring dB down. Sound quality and level are very subjective. I LOVE the sound of my [full] Termignoni system. There's something about Desmo + Termi+ Ohlins working together in harmony!
Case in point, this small can is going to be quite a bit louder:
than this can:
Weather or not it brings it into a level acceptable to you is a different story.