Your walls, as designed, are so far beyond "fire rated" it's funny. Just build 'em and fuhgeddaboutit... :=))
Seriously, no prob - and, fire
CODE is a
TYPE of wallboard with a different formulation, so that THIN stuff can meet fire
RATING, which has
NOTHING to do with formulation. Fire
RATING means, this frame, this insulation, that wallboard in this thickness, is
RATED to withstand a fire for 1 hour, 2 hours, etc - I'm not even sure they
HAVE a fire rating for THREE layers of 5/8 gypsum, no matter WHOSE brand/type it is. You may obsess about something
ELSE now...
Kinetics Kips; haven't used 'em, but WSDG has (and doesn't hide the fact) - since they are compressed fiberglass, I'm not sure what all would react differently. Life should be good, I've no idea about compression range vs. lifespan. Kinetics, similar to Auralex' UBOATS, just says "put 'em in and do your floor", no calcs, no nuttin' - I tried to get Jeff at Auralex to say why they did that, and got stone-walled

haven't talked to the Kinetics guys about it.
AFAIK, you would still need to stay within a range that wouldn't allow the pads to either LEAVE compression or BOTTOM OUT under any circumstances, but beyond that as I said I don't know yet whether the fiberglass pads have the same limitation as EPDM, etc, as far as staying toward the LIGHT side of loading for longevity... Steve