Kickdown band lever ratios

It used to be that the 5.0 was the way to go. I've one in my slant 6 904 for over ten years now. When I was building my NSS/E 65 Belvedere, Ric at A&A said to use a 4.2 and not a 5.0. I can't remember why . I hope someone chimes in with a answer. The 904 I have now has a 4.2 in it also.All of them had manual valve bodies.