Being tall as a girl *will* draw attention to you, however I agree with everyone else that it is possible to pass even at 6'4".
I am 6'0, 170lbs, never taken hormones so I have a masculine physique (not overly muscular but more toned than any females except perhaps professional athletes). Yet I pass in almost all situations because I was lucky to be born with a feminine/androgynous facial structure. Typically the only times I get clocked is when my voice slips.
It is true what they say, face/voice is the deciding factor whether or not you will pass. Height or masculine physique will draw attention to you but as long as your face/voice are good enough you can still pass. I would say that the taller or more muscular you are the better your face/voice needs to be in order to really pass. I know it sucks for those of you who are really tall with masculine facial features but on the bright side at least face/voice are things you *can* change, unlike height, shoulder breadth, hips, etc.. Yes it may take a long time saving up for FFS and practicing voice/mannerisms/posture, but I believe almost anyone can become passable given enough time and effort.
Despite being lucky and not needing FFS I never thought I would be able to pass the way I do. I thought my height, shoulders, big feet, etc.. would be a dead giveaway, but in practice I have found those things don't really matter, people are hardwired to gender you based on your face primarily and most people will overlook even the most obvious clues as long as your face/voice are decent.