G
The 5's are just a better speaker. No doubt about it, but I own the Quatro and feel that they are also very special. Honestly, to me, I feel strongly that the Quatro is the sweet spot in their line. Would I have liked a carbon fiber midrange too? Yes, I would have, but for ME, I just couldn't afford the 5's. IF you have the money, then you will get a much better speaker in all aspects. The bass is bigger and that midrange with the matching tweeter is incredible. Personally I feel that the 5 is a GREAT bridge between the Quatro and the 7. It should be selling for over 40k and the Quatro should be in the 25k range (with a carbon midrange upgrade).
That all said, I did put my money where my typing is and got the Quatro and am not looking back.