Thanks for the replies.
rdtompki, Interesting that you found the salmon to squeal less than the duals. Koolstop's page here,
http://www.koolstop.com/brakes/Compound.html has a comment at the bottom that suggests that the reverse should be true.
IIRC the salmons are slightly cheaper here than the duals so I may go with those to start with and see how they are.