Diff discussion

Hi all.
my Chrysler currently has a 2.92 open wheeler diff.
at 100kmh or 62mph it’s doing 2,600rpm!
that’s with a 727 trans behind my 318.

now I’m hoping someone will have an idea on this as google hasn’t come up with much I’m afraid.
I’m wanting to change my diff ratio to either a 3.23 or a 3.5 but can anyone tell me just what revs I’ll be pulling at 100kmh or 62mph with either of these two please.
????

if it helps my tyres are a 235/60/15
Author: Shano