This question come up a lot but the real question is what is acceptable to you for a 60mph cruising RPM and what is acceptable for off the line acceleration. For my self I like the reliability of a th400 so a 4sp auto is not an option to me. I have had 3:36, 3:23 and 3:42 in my two pontiacs and now with my advancing old age I'm gathering parts to put in a 3:08 gear. Keep in mind the 455 has lot more torq and doesn't need the steep gear as bad as a 400 or 350. In your case I would lean to the 3:23. I had them in my 77GP w/400 and it was a good compromise.
From what I recall at 60 mph and depending on tire size: (maybe some other can fill in here too)