I've seen 122 as the "normal" temp for a protein rest, and Noonan says the protein rest should be 122-131. He does say that at the lower end of the range, polypeptides might be denatured, reducing the body of the finished beer. The protein rest is really crucial for poorly modified continental lager malts.
With modern, well-modified malts, I'll usually only do a protein rest for 5-10 min to avoid excessive polypeptide degradation.
Long sac. rests aren't a problem. It just gives the enzymes more time to work. During boiling you might liberate additional starches, so I'd let it sit for another 15-20 min after adding back to the mash, before mashing out, to make sure any new starches are converted.
To paraphrase Dr. England - "Off-flavors smooth with time. So do mountains. Brew it right from the start!"
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