Re: new sound
The short answer to your question is "NO", you can't find a great jazz sound in a mouthpiece. A great jazz saxophone sound can only come from lots of practice and experience and LOTS of listening. I'm not saying the mouthpiece doesn't matter, but you're not going to get a great jazz sound by only focusing on the mouthpiece.
One of the best things for developing a great JAZZ sound is to transcribe solos. Start with players who have big sounds and play accessible lines like Dexter Gordon, Ben Webster, Johnny Hodges, Cannonball, Stitt, etc...... This helps you internalize the concept of what a good sound is. When transcribing a solo you play over the top of whoever you are transcribing. In doing so, you should really focus in on their inflections, dynamics.........basically try to copy every bit of expressionn in what they are doing. The goal of this is not to come away with this persons sound as your own, but rather to learn what it takes to generate a good sound. Your own voice will come out in the end.
Its also key to starting each practice with at least 5 minutes of long tones (10-15 minutes is even better). There are many different long tone exercises and most all of them are good. Don't spend too much time debating what type of long tone exercises to do, Just do it!!
Lastly, you want to consider mouthpiece. Since you already have a Meyer 5, you have a piece that will take you a long way in straight ahead jazz. Assuming you're doing the above and you're still not happy with your piece, I would recommend finding a shop that has lots of jazz mouthpieces in stock where you can play test and then go in and play them all. You'll learn a lot about mouthpieces by doing this. As for metal, try Otto Link and Dukoff. Ponzol, Warburton and Jody Jazz are also making very good metal pieces these days. Although, its a little harder to find places to try all of these.
Best of Luck!!!