Subject: Re: 401k
The only financial benefit that comes in is if your marginal tax rate NOW is lower than it will be in the future. Which is not often the case.

I think it is the case for nearly everyone (everyone who is married and middle class or higher) at some point in their life. Usually beginning the year after their spouse dies. When married filing jointly for the first X years of retirement, your tax rate is usually lower than it is for the Y years of retirement after your spouse has died. So if you do the conversions, and they otherwise make sense of course, during those X years, then you will likely be better off overall from a tax perspective.