This is a great choice!
There was, indeed, a great rivalry between these two. Samantha had been a topless model in the British "Sun" newspaper, and then Sabrina did a nude feature in "Mayfair", a British men's magazine. Their rivalry continued when Samantha built a career as a singer - Sabrina was already a singer, and she referred to Samantha as "that small-breasted British midget" {Samantha is around 5 ft tall]. As regards breast sizes, they were pretty equal - around 36D/36DD, depending on which publication you read.
As far as a fight goes, I think Sabrina would win, although it could well be a close-run thing.
GG