20 years, 5% returns, $6000 annual contribution means you'll have about $200k in the Roth, $120k of which will be from contributions, resulting in 4% SWR of $8000. Roth contributions can be withdrawn penalty free before 59.5, so you'll be able to withdraw $8000/yr for 15 years. That's cutting it somewhat close and while the $200k is probably inflation adjusted, the $120k isn't, so you're probably right that you want some available in a taxable account. I would still max out Roth unless that's everything you're saving.