I recommend you look at I-ORP and use the extended analysis feature to optimize withdrawal and spending in retirement. You can play around with the tool to determine if Roth conversions would optimize your situation.
I urge folks to think really carefully about what we are really seeking when we say "best outcome."
I-ORP or a SS breakeven calculator can show us which course of action will likely to produce the highest average monthly payout/portfolio value, and people latch on to that as the answer. It
sounds like the answer. But consider this example:
I am offered the chance to take up to my entire portfolio and risk it on one a flip of a coin. If I guess right, I'll be paid 3:1. If I guess wrong, I lose my money. How much should I bet?
Going strictly by the numbers, I should bet every penny I have (and borrow more if possible!). There's a 1:2 chance I'll win, and I'll be paid 3:1. It's a fantastic offer, free money.
But in the real world, I would probably bet very little. Yes, it is a fantastic opportunity. But if I bet my whole stash and lose it, the negative results are terrible: depending on handouts for the rest of my life. If I win, the positive results are very nice (tripled my money), but that extra dough doesn't have nearly the utility I am risking (my initial stash, which was enough to keep me comfortable in my retirement).
The first dollars in one's portfolio (or monthly check) have a lot higher marginal utility than the last dollars.
So, when considering whether to pre-pay taxes now vs. waiting to pay them later, I try to consider this. It's not a simple math problem. If I'm in the 12% bracket now (MFJ taxable income of $19K-$77K) and I wind up in the 22% bracket (MFJ taxable income of $77K-$165K) in retirement, it probably means my annual take (i.e. monthly income) is a LOT higher than my income today. Lower marginal utility of those last (much more numerous) dollars is fairly low, and paying taxes at that point should sting fairly little. OTOH, if my investments do poorly, or I have to deplete my portfolio for unavoidable spending (sick child, spouse, etc), and I find that our portfolio is really in trouble, I may very much regret voluntarily reducing my portfolio in years past to give the IRS a bunch of money. That money could prove really useful to me (i..e each dollar in my portfolio and in my monthly income has very high utility to me) , but I don't have it anymore.
Now, I'm sure that a smart economist/accountant has already figured out how to quantify these things, and I'd
love to see that spreadsheet/calculator.
Apologies for the wordy response.