While in theory we could have one answer, i suspect the answer is different for transwomen and transmen. Sadly, transwomen are at FAR higher risk of violence from a partner who feels 'lied to'. Because of that, transmen probably have the ability to wait a little longer, while simply not escalating physically, until they trust the person.
Transwomen unfortunately are in a situation where they are trading off two factors. One factor I don't think should be considered much? the fact that many people 'won't give them a chance'. Heteromales in particular are not very likely to 'give someone a chance' if they weren't open to it before hand. My impression is that women are a little more likely to be open to it if the connection is there (and my rusty brain suggests even GaG polls have supported that).
So what are the factors? Factor 1 is that if you wait too long, the person may feel lied to and be hurt, or fly into a rage, which are both bad for different reasons. Factor 2 is that the transwoman may not want everyone on the planet to know and may not want to tell their history to every damn person in the world.
So I think:
- if they're okay with it, A is 'safe'.
- if they would rather be more careful, I'd say B, or maybe 'B-'. They key is to say 'i like this person enough that even if they can't accept it, i trust they won't treat me like shit, and if i suspect they would, i'd just stop seeing them'. You need to delay anything even a kiss beyond that point though.
My impression is transmen can go closer to C. Whether that's 'right' or not, i'd suggest asking women, not me. But for transwomen, i think C is too dangerous.