Hi Patrick,
Thank you for sharing your encounter with those marvels.
I must confess that each encounter of a Patek Philippe minute repeater leaves me a strong impression.
I'd be interested to know in which catalog you read that ref 5078 can be ordered with cathedral gongs? 
Only two models currently house the cathedral gongs AFAIK. The 5002 is the "extreme" Patek Philippe and the 5074 is also larger than the more classically sized 5078 or 3939, due to the room needed to house the cathedral gongs. Ref 5078 replaced ref 5079 which was a 5074 case with a 5078 styled dial and a 5078 calibre with cathedral gongs.
My very little experience of cathedral gongs has been very positive, even compared to "normal" Patek Philippe gongs.
Maybe the ultimate Patek Philippe minute repeater (for me) would be a 37mm 3939 with only cathedral gongs added to the (for me) already perfect 3939, keeping the same style of case, dial and hands? Who knows?
Regarding quality of sounds, out of the improvement brought by the cathedral gongs, I've never felt an order of references as the sound of a minute repeater can (and should) vary from each specific watch to another. Among non cathedral PP repeaters, I didn't really notice a significant difference.
If I had to ever own a Patek Philippe minute repeater, that would be a white dial in platinum case (but I've yet to see a pink gold one). If I could get a second one..... 
Cheers
Dje