When I've questioned myself, I've come up with different sorts of questions, more along the lines of what rejennerated asked herself:
Would I still be a man in a society where men wore pretty clothes and grew their hair long? (yes)
Would I still be a man in a society where men had lower social status than women, couldn't work, couldn't own property, couldn't vote? (yes)
If, when I was growing up, the softball team had been all boys and the baseball team had been all girls, and baseball was the sport played professionally, would I have played softball or baseball? (softball - in reality I played baseball with the boys)
I asked a lot more questions like that. The only stumbling point for me was imagining transitioning in a society where gay men are executed. I could deal with a homophobic society, but not so sure about one that would want to kill me. But then I thought about whether I'd want to be a woman if I'd been born male in such a society, and the answer was "hell no!" So I gave myself a pass on that.