Someone with the actual numbers will need to chime in here, but it almost always 100% of the time makes sense to do the Traditional/pre-tax instead of the roth. That is because you can drop your taxable income now, and minimize taxes in the future via your lower MMM cost of living.
I'm not familiar with the Roth 457 rules, so I can't really speak to that, but two things come to mind. 1) one of the major benefits of the 457 (as I understand them) is withdrawals after employment severance without penalty regardless of age. It would be a shame to loose one of the major benefits of the 457. 2) As evidenced by all the threads about mega back door roth iras, etc, there is usually a loophole for getting the money out and minimizing/avoiding penalties. It sounds like you've got some research to do.