I think 4.30 is a workable choice, especially if going to a taller tire in the future. I might have chosen 4.10. I have had 4.56s, 4.10s, and 3.91s in mine, and it didn't change E.T., but I've got a 440, and spinning it real high rpm is counter productive.
Seeing that you have a nine inch, are you gonna run a spool, or some sort of lsd? Ford "posi's" are not some of the best. I have a spool in one of mine, gonna try a lock-rite in my other one.
If you don't want a spool, imo a Detroit locker would be the best choice.
