Green Glue or another layer of 15mm Gyproc?

I'm constructing a home studio and was planning on using RC1 Resilient channel with a layer of 19mm Gyproc plank and 15mm Soundbloc Gyroc with a layer of GG in between. However, seeing the cost of GG, I can install another layer of 15mm Soundbloc for half the price of the GG. So then I'd have three layers of Gyproc just screwed together. What are the pro's and con's of this approach (apart from cost)?

On a single-stud wall, GG wins hands down, but on a decoupled stud wall, adding an extra layer of 5/8" drywall is roughly the same as adding Green Glue in between the first two layers, although GG is probably still a few points better. The disadvantage is that the extra layer of drywall takes up extra space, and puts extra strain on your structure. The advantage is lower cost. Toss up! - Stuart -

Green glue it is then! Also, it saves the hassle of fixing another layer of Gyproc. I'm at an age now where my time and a hassle free life is of more value than money :D