Back to the original question:
When I finally took the plunge and transitioned in the autumn of last year, it was when a number of factors had run together:
1. Over the summer, a woman I met told me that she didn't know I was trans until I spoke up and said so. This gave me pretty much all the confidence I needed, even if I wasn't 100% positive that I would succeed 10 for 10.
2. I felt increasingly unbearable pressure from within that was making it impossible not to transition. In fact, this alone would have pushed me to go ahead, ready or not.
3. I was outed to my boss, and he strongly encouraged me to go ahead and transition immediately.
So here's the cool thing I discovered immediately, from my first day of fulltime:
I began "passing" 10 for 10 because the act of transitioning itself gave me such a psychological boost that everyone now saw me as the woman I am. Hypatia says: Take the plunge!
"Whatever you can do, or dream you can do, begin it.
Boldness has genius, power, and magic in it. "
--Goethe
I can't emphasize that enough. Taking the plunge was the key step that boosted my personal transformational magick to succeed in transitioning and "passing." Like I said above, if I'd waited around until I thought I was already perfect, I'd still be waiting. Instead, I just went for it--and it worked. YMMV.