Excellent points. For myself and my development team, I enforce an 80/120 rule: "stay under 80 characters whenever practical; stay under 120 characters at all times".
The reason for the compromise is, one shouldn't sacrifice good coding practice and style to adhere to this! It's a rare phenomenon, but once in a while, you'll see a maddening piece of bad practice whose only justification was "80 character limit!" Still, I've yet to see an exception to 120-characters, ergo the 80/120 Rule.
I go with 100 on the soft limit, and treat 120 as a soft, but stronger limit. There are always some odd cases where it ends up being better.
For comments/api-docs I actually prefer having no limits at all and relying on auto-wrap. It's more natural to write prose that way.
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