I doubt anyone could give odds on that. You only need it once right? When my partner looks back, she explains it this way. I fell in love with you (when I was in male mode). I saw how being that person was very painful for you. Now that you have transitioned to living female, the things I saw in you originally, are no longer overshadowed by your pain. You are now the person I fell in love with.
It is tricky to know when to tell someone. I tend to be on the side of being honest early. Then again if you are letting someone get to know you, I see that it might be wise to let them see your personality before factoring in the T word. I don't see that as dishonest. If you develop a more personal relationship, telling earlier may lead to less thoughts of you having deceived them.
Monica