mutt, good to hear from you again.
Well, that's a good question and what I'm working to find out. The GIII's cumulative noise margin beyond Stage 3 is actually 9.3 EPNdb - 2.1 above TO, 8.6 above sideline, and a credit of 1.4 beating Stage 3 on approach.
As long as I can show NAC and avoid noise testing, the only one I really care about is a reduced flyover/TO noise, and I'm hoping to get that down considerably with weight reduction. Not too much, obviously, because I'm chipping away at the airplane's utility. I'll know more when I've figured out the TO path/profile comparisons.
Bests,
Tom