Has anyone seen a Roth 401k calculator that compares contributing to a Roth 401k vs a regular 401k for X years and then withdrawing Y years after that?

I am trying to show a friend that despite the extra taxes now that she would be better off in the long run to contribute for a few years to a Roth 401k. Her 401k is large and she will not need to tap the Roth until long into her retirement if at all. Bankrate, Fidelity & Schwab among others have conversion calculators but nothing this complex.

Thanks