Just for the record...Your last quote confuses me, reference NGFS being not exactly common? Correct me if I'm wrong but if we look at the last thirty odd years with regard to Destroyer / Frigate main gun armament usage in 'real' combat scenarios the NGFS role has been dominant, from the Falklands through GWI & GWII. When was the last time the primary gun on any post WWII vessel went toe to toe with an enemy fleet (not counting some abandoned dug smuggling vessel or pirate skiff) or shot down a fixed or rotary wing aircraft?
BBC ON THIS DAY | 24 | 1982: Battle for the Falklands
" could actually see the missile heading straight for us at about two miles. We hit it and destroyed it with a 4.5 shell." However I have heard it was the A4 that was shot down an not the missile but that is unreferenced.
Another from wikipedia
"English: Spent shells from a naval gunfire support mission by HMS Cardiff (D108) on the night of 5 June, 1982, as part of the Falklands War. Photograph was taken the morning after on 6 June, also the top of her charred Sea Dart launcher can be seen bottom right. She fired 277 rounds that night[1] and also shot down a friendly helicopter."
How many times has the RAN NGFS in the last 50 years? Its not exactly common, I stand by that statement. Im not saying its unimportant or ineffective or its not going to occur in the future.
The AWD for example will be 5". ANZAC II will most likely still be 5". Tomahawk, UAV's, Tigers etc are going to lower the need of NGSF (but in no way eliminate it). Conversely, 6" could end up better guns with combined development, lower ammo costs, shared costs, greater burst rounds, greater penetration, more sophsicated guidance, longer range etc.
I like the fact that naval guns are getting larger again, it does make perfect sense to go to 155mm. I hope it happens for the RAN and they should plan to do so as much as possible.