Another aspect, often missed in such discussions (and I did not see a word about it in this thread), is the cost of opportunity paid during Roth conversions.
The goal of the conversions is not merely to minimize income taxes paid during retiree's lifetime (as many of the more simple-minded individuals wrongly see it), but is instead to maximize the efficiency of one's portfolio.
Which is done by ensuring that most of the portfolio ends up in one's pocket to spend, give away, or simply waste. The money not ending in one's pocket are just friction losses and include portfolio expenses, income taxes paid, and whatnot...
Thus, if the retiree aimed at higher efficiency, (s)he would also take into account that all extra income taxes paid due to conversions are amounts which disappear from one's possession annually, and once each of them does, it is unable to produce any future income.
Were these amounts not spent on income taxes for conversions, they would have been generating future income streams, a very welcome state of affairs.
This cost of the lost opportunity would need to also go into the equation.
Most people ignore it. I don't.