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.
The First Doctor would know that regret as well.
"Eccleston was a tiger and Tennant was, well, Tigger. Smith [is] an uncoordinated housecat who pretends that he meant to do that after falling off a piece of furniture." - Lynne M. Thomas
"I'm in Hell and it's full of Avons!" - Vila