I had a sample of 1950s (?) no.5 extrait. Gosh. It had a real musky, animalic kick to it that I don't find present in the current formulation. If you can find a vintage bottle in good condition and for a reasonable price, I'd say go for it. That said, I still like the modern version.
As for Arpège, I've only smelled the 70s extrait (thanks, L!). Huge powdery floral (jasmine, rose if I remember correctly) that seems to get progressively sweeter. Good fun to sniff, but not quite my style. I'd be interested to hear comparisons with the current version too.