This statement here is a defining factor: "You have $100K you can convert to a Roth. Do it and you're left with $80K"

I take a person's age into account, as Greta describes. But the other issue is how the conversion is "paid" for. If I convert $100,000 there will be $100,000 to grow at 8% per Bob's example. Specifically, I would never recommend a conversion when a distribution is how they will fund the taxes.

If a person is going to have the added taxable ordinary income and also pay taxes (even though playing within tax brackets), and they are old enough or cautious enough that there isn't a lot of expectation for good growth riding out bad times, then why convert? They won't have that different of a financial position in a few years, other than maybe hitting RMDs.

If someone is in the prime earning years, say mid-50s, they have 10-12 years to convert; spread it out. It doesn't have to be all at once. They would be moving the funds before the added AGI hits for IRMAA. They have plenty of time in a variable market to find earnings and growth (20-25 years to RMDs).

It really depends on why they want to convert: avoid RMD, tax free growth, beneficiary benefits.