Any break even point less than 3-4 years out is the better deal between costs and rate. This does not take into account the tax benefit of paying points, or the tax consequence of a lower rate versus a higher rate. That kind of math has too many possibilities and with infinite options comes infinite confusion. I defer this kind of calculating to USCCPA
If you are likely to retain the property for some time try and pay for the lowest rate you can today. Any rate, sub 4.875% is a screaming deal. It's essentially "Un-refinance-able" seeing that you'd have to get a zero fee refi rate sub 4.0% to make sense to act upon. I do think it's smart to buy the rate down because you're likely to hang on to the property for a great deal of time. I am in this scenario assuming little if any appreciation so selling to move up won't be as likely as we've seen in the past.
My .02c
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