I have seen EPDM more often than Neoprene. I don't know which is better. I don't have the experience to do load calcs but is would imagine that the width changes the amount of compression. I have seen resilient sheets and MLV and Green Glue recommended between layers of plasterboard. Since they are screwed together in any case I doubt that there would be much difference. However, Green Glue at least publish some numbers, so if you do the screwing and glueing as they say I guess you should get the extra they claim. How about using high performance Resilient Channel as well as the proposed floating stud structure. Here's one.
WallComp, UK - CMS Acoustics
Lots of other acoustically chosen products on that site also.
DD