Because the old PAF pickups were handwound there isn't just one authentic vintage sound - some were overwound, some underwound, some might have an offset between the two coils. And they used different magnets - Alnico II, III or IV (as Tim has mentioned elsewhere).
57 Classics are good pickups but they're only one "flavour" of vintage PAF - Mules, Stormy Mondays or many other manufacturers' PAF replicas are no less "authentic", they're just different. I think you should get whatever sounds best to you.