There is one more tangible difference... you don't have to alter/cut your rear diffuser thus keeping it stock.Surferjer said:I think they sounded similar for loudness. The comment I heard from others was that the QS sounded "throatier", but necessarily louder. I can't define "throatier" except IMHO the QS sounds more ragged and edgier. I'm not describing it well. And I don't know how the Stage 2 sounds under load. If Stan and I were thinking, we should have swapped cars for a brief drive. Then we could have compared under load.
To me the bottom line is you can't go wrong either way. Try to get a listen and go with your preference. The only tangible difference (if you put Stage 2 on yourself, making the cost the same) is that the QS if 4 lbs lighter. Not a big deal.