asianautica- you would have to be in the highest tax brackets for Fed & State and get around 4.75% tax free from the muni’s to see an 8% taxable equivalent. I’m not sure what current muni rates are but I doubt they are in the high 4%
For example: Say your total effective rate is 41.045%
Select a tax-free yield on the left, and look across to find the taxable yield you would need to get the equivalent after-tax return.