There are some basic points that make the difference:
1 - Superman as the real identity in Pre-Crisis;
"Clark decided he must turn his titanic strength into channels that would benefit mankind, and so was created...Superman!" gets repeated a lot in the early stories. Clark comes first. To me, the keys to "1" are:
- Does Superman live longer than regular humans do? If he does and he knows he does, then Clark is either a fiction or everyone slurps from Infinity Formula while basking in their own Lazarus Pit. Given comic book time, I suspect the latter is true.
- When does Superman find out who he is and where he came from? Pre-Crisis, he knows he's different early on, but how and when he learns where he's from has morphed. Some aspects of total recall and full command of language at age 2 are scar-for-life frightening.
- Does Clark really "matter" to Superman? If someone who knows his secret were to ask him "what's your job" in close quarter, would he say "to write a news story" or "to fight crime and evil". How often does he speak of Superman and Clark in the third person?