My assumptions:
$2.2M Traditional, $100K Roth to start. I started converting as soon as I FIRE. I'll be 48, but wife will be 53, so I used 53 as the starting age. From 53-60, I have no income except for the conversions up to 22%, as I will be living off of taxable accounts. At 60, I start taking my income either from the ROTH or the Traditional. I ran both scenarios to compare. It seems at a 3%+ real return, all I'm doing is trading taxes for market gains. At 2% there is a benefit, which starts at age 72. I also have assumed tax rates do not change. And again, my income needs exceed the RMD. For instance, in the "do not convert" scenario with 4% average return at age 70, after withdrawals the value of the Traditional would be $2.032M. So, the RMD would be $2.032/27.4 or about $74K. I assume I need $125K income, net of taxes. So, if it's coming out of tIRA I have to withdraw roughly $150k.