Chris - Thanks - you just got in before me:
Just to note the Dart is a single spool animal - prop is connected to the one (and only) shaft. 2 stage of compressor (centrifugal) and 2 turbine stages though - perhaps that's what you were thinking of?
My only recollection of a Proteus (thread drift; pull up!) is the rumble I used to hear from miles away when a Redcoat Britannia used to make an occasional visit to EMA. I always wondered whether 'Whispering' referred to the experience seated within, or watching it go by.
Cheers