Trick, this is exactly why I posted this. I did an over/ under split-system A/C install today and was talking to the HVAC contractor. He saw me looking at the specs on both CU's and told me, "just run a 30 amp 10/2 wire."
So I said, "ok, but I could really just run 14 wire and it'd be ok by NEC standards."
He says, "I've never heard of that so don't so it."
(this coming from the HVAC guy, not an electrician)
Of course, the better install is to run the maximum size wire and the maximum size OCPD, I'm sure most would agree. But the point is, it can be done and pass inspection, and damn it felt good to hold my own in this discussion.