Yes, your thinking is on the right path, but that 6% state tax makes it less of a slam dunk.
What tax bracket do you expect to be in when you retire? What about state taxes? Will you move to a no or lower tax state?
I expect to spend some time abroad after establishing residency in a no tax state, so I figure anything under 15% when considering state+federal is a good idea because the 12% bracket is set to revert to 15% in 2025 unless it's made permanent. I'd be willing to go higher if I expected to always be in a state with an income tax, so I guess my thinking is I'd consider converting up to 15% + expected future state tax.
Of course, if you expect to be in a higher bracket in retirement, go higher, but since the 2nd tier tax bracket (was 15%, now 12%) goes to around $100k, I think that should be a more than sufficient withdrawal for a mustachian.
Marginal rate now and marginal rate at retirement is all that matters. What you're at in between doesn't matter one bit.