Re: A thought on regenerations (spoilers for "Night/Day of the Doctor"
Since you mentioned Caves
, I think what made that one really powerful was the Fifth's last word being "Adric". It kinda summed up the entire incarnation, right there and then - a regret only 8 (via BF) and 10 would know about.
"Spock...?" Kirk said, whispering.
"I am... most pleased to see again, Captain" Spock formally replied.
McCoy shook his head in disgust. "Oh, for crying out loud, Spock. Its been eighty years!"
"Seventy eight point four years, Doctor."
The Holy Three meet again, in The Return