I think some of the stated difference in brain size that are noted between a male (testosterone) and female (estrogen) dominant brain environment has to do with the amount of the brain dedicated to spatial-visual skills. Estrogen dominant brains are usually about 10% smaller than male brains, which is why head size can be a limiting factor when it comes to "passing", males usually have bigger noggins.

This makes sense if we hypothesize that it is these visual spatial abilities that change, becuase the amount of "hardware" needed to map your environment in 3d and consider trajectories, displacement, etc is massive. In a conventional computer for example the part that will draw the most power and have the most transistors in a given die area is typically the video card, the part responsible for rendering the world in 3d. Perhaps this makes sense if we consider that from an evolutionary sense men are most likely to be hunters while women will have a more well developed communication and empathic capabilities in an estrogen dominant brain since they would share the child-rearing and other communal tasks more?

I suppose the best way to get some idea if this theory holds any water would to be to ask the girls who have been on hrt for at least a year or so if they have experienced any changes to their visual-spatial skills. Is it harder to parallel park a car now?

As far as sexual orientation changes I really don't know if one can simply blame it on estrogen. In the past homosexuality was attempted to be "cured" by administering hormones and had no effect.

Also as far as the effect of hrt on a genetic male a good place to find out what a typical man would experience is to visit support forums for men who are being treated for prostatic cancer with androgen blockers and estrogens. None of them decide they are women or change their sexual orientation. If we consider women who have had total hysterectomies and don't take hrt for health reasons one can also find support forums on the net for folks in this situation also and I have yet to find someone who reports it has changed their sexual orientation, although it is common for people to report that they lose much or most of thier libido in this situation. I'm sure their are always outliers though, because one of the most insatiable women I have ever known had already had a total hysterectomy. So who knows? Best to just say ymmv.

I wonder if the main benefit of hrt is simply allowing one's physical body to become more like the image that their brain has always expected to see in the mirror.