I've been in touch with Nick and asked him to drop by, so hopefully some informed opinion may be coming soon!
I recall that the 76A was 100%Nr across the board until an advisory notice appeared advising of the added performance available in the cruise when using 107%Nr, but maintaining 100% for T/O and landings. There may also have been an altitude associated with the 107%, the grey cells are struggling but was it >5,000ft?
Having established a fair baseline of ops at 100% there was no doubt that 107% gave a cruise performance improvement of some 3-5KIAS and most of our ops were 7-9,000ft out of Essendon. All for the same fuel burn, too.