The series-era McCoy was cooler under pressure (and for me, the most admirable character, because he stood with his friends in really bad circumstances even though he clearly did not have the resources to defend himself as they did -- something that they got seriously right in STAR TREK 5 when he faces down 'God' after seeing the punishments meted out to K & S.)
Truer words were never spoken!
Even in Space Seed
, with McCoy standing up to Khan (with a knife at his throat, no less!), "Well, either choke me or cut my throat, make up your mind!" , and "It would be most effective if you cut the carotid artery, just under the left ear." He had to be the bravest of the cast in many ways.
If skinny little me is ever confronted with such danger, I hope to be able to channel McCoy!