I forgot to mention that Gander International Air Radio also transmits on 127.100 and 126.900 from the Gander location.
These two frequencies are used by Gander to provide HF frequency assignments and obtain SELCAL codes for the Atlantic crossings. Still done by voice and not datalink, for now. Much the same as the dedicated New York ARINC feed on 129.900 in the New York area for flights heading down to the Caribbean.
These two frequencies can be very busy during the eastbound rush so best to put them on a separate dedicated feed if possible. (Throw in some voice recognition software and use it to auto-tune the HF feeds with the current primary and secondary frequencies - now I'm getting carried away).
If 4 feeds can be utilized I think this would work nicely ....
Feed #1 Airport
123.475 Gander FIC (domestic)
126.700 Gander FIC (domestic)
Feed #2 Gander International Air Radio
Feed #3 Gander Center Low FL280 and below (also works arrivals/departures)
Feed #4 Gander Center High FL290 and above
As for adding all the adjacent Gander/Moncton high frequencies I don't know if this is a good idea ? There are about 14 more frequencies that could potentially be on the fringe of reception, with weak signals. The nice thing about Gander is when they combine these adjacent sectors the frequencies are cross-coupled so you would hear the aircraft loud and clear anyway. This would vary throughout the day and depend on the locations of the NAT Tracks. I think it would provide a better listening experience without getting a bunch of weak hard to read signals that could block out same 5/5 transmisson on the cross-coupled frequency. It would depend on the type of equipment and reception range of the Feed ?
My 2 cents (more if you need a donation).