Many thanks your advice pm... I had a conversation with a np team rider today who said exactly what you mention on my questions
I will actually have to get a 430 Sdm mast with 48cm ext to work correctly with my 6.9m firefly
Also discovered it was not the best sail for a beg/int sailor on flat water as more a wave sail....
As you say it is important to do your homework before getting caught up in a sales pitch. ....