Had a look in my files. Found a 19 page article in 'Aeroplane' of December 2010 about MB fighters, written by Tony Buttler, in which it says:
No mention of Dagger VIII in Tony's article.
Bill Gunston wrote an 8 page article about MB fighters in 'Wings of Fame' Volume 9 that mentions Dagger III but not Dagger VIII and no mention of boost either.