Hmm. A quick scan of your prior posts indicates 1) You live in MA, which taxes STCG at a whopping 12% and has an exemption for MA bank interest, doesn't it? 2) This question of what to hold in taxable is a well trod path; and 3) Three years ago taxable comprised only one quarter of your assets, and your plan was to grow taxable and tax-advantaged at about the same dollar rate per year.
So I'm wondering why not munis in taxable when your combined tax rate is about 33% and will go up next year? And why can't you fit all your bonds in tax-advantaged (not that I think that's necessary)? Also, can't you hold about $20,000 of your bond allocation in a MA bank CD and escape state tax on the interest?
Here's a recent thread that may be of interest (but note that it ignores the peculiarities of the MA tax code, which I think slightly amplify the advantages of bonds in taxable): viewtopic.php?f=10&t=106053