Bryan,
Yes, Green Glue does have a lot of technical data to support their product. However, I didn't notice any tests that compare GG to butyl rubber caulk. There's a GG/construction adhesive test but construction adhesive, after it drys, turns into a relatively hard mass compared to butyl caulk and I presume GG. In fact there's no test that compares GG against any other flexible adhesive caulk.
GG when compared to engineered panels is slightly better but requires the installation of double layers of 1/2" drywall so the comparison is flawed. . I wonder what the test would conclude if you used 1" engineered panels. Also the extra labor required to install double wallboard is an important cost factor.
I suppose that the cost of GG, when looking the whole project, is a small price to pay even if it's just green colored premium adhesive caulk. At $7/tube it's really not much more expensive than the 4 or 5 dollars for a quality alternative.
Just a skeptic here. Well...enough splitting hairs for the day. 
-Roy
Compare the COST of a 1" engineered panel - not to mention the 4 guys it will take to lift and install it. 2 layers of 1/2" and Green Glue will be way cheaper and way easier to put up.
Believe what you will - I can't convince you otherwise. I don't know what butyl caulk would do. I DO know what Green Glue will and has done for many of my customers. It's never, ever the weak point in the isolation scheme by a long stretch.
Not to be a smart ass but I don't see a comparison to peanut butter either. Seriously, people have been doing isolation in recording studios for years and there are a lot of things that have been proven to work and not work. They've used mass loaded vinyl, tar paper, etc. Some work, some work better, some don't work. Those that people still try to use don't include caulk. I'm quite sure people have tried it before. If it was all that, it would be all over the studio forums - it's not. Sure, you can do something for 1/2 the price and it might work 1/2 as well. Might not. It's something that's very expensive to try and then have to try to undo. I'll go with what's proven when the alternative is ripping down walls and starting over.
The seams for the first layer should be caulked, then taped and mudded - at a minimum, a fire coat. It's not just about air, it's about additional mass. Every bit helps. It also helps minimize the additional gap between layers where you have the recess for the tape to fall.
I'll agree that staggering seams is critical.
Bryan
