Just back from PE sooo....
HP IK (inc. twin scoops) and exhaust 122ATW 141lb/166ATFW
HP IK, exhaust and fuelling 140ATW 154lb/174ATFW
On the first run, I did see the ATW figure drop from 129 so even using that higher figure as a bench mark, the HP mods seem to work and are in line with my expectations.
But this still leaves the differences between the 172s a mystery......