I'll WAG at 50%.... But I'm also going to add some commentary.
Of the total number of males who have transgender identities, I wildly speculate that 20% of them don't use female restrooms at all, because they actually respect females. Take that with a grain of salt, add or subtract to whatever feels right to you.
Of the remaining 80%, let's say that only half of them are pervy. I say pervy not as a judgement on transgenderiness, but a judgement on males of the human species. Required "not all males" disclaimer. At the end of the day, males are simply pervier than females. It is what it is.
So let's talk about the remaining 40%. Of those, I would guess that at most 1/4 of them are old-school transsexuals who've put in the work and the effort and arguably pass well enough that they can get away with it, and it's the most rational thing for them to do.
The rest of them, however... even if they're not perving about it, they're intentionally violating female boundaries while knowing full well that it makes females feel uncomfortable and threatened, and they relish the power they have to force females to bend to their will. They're exerting a very masculine kind of power to intimidate and control females for their own benefit.
In summary... out of the entire population of males with transgender identities:
- 20% don't use female restrooms out of courtesy and respect
- 10% are old-school transsexuals who pass well enough that it's the rational thing to do
- 40% are pervs
- 30% are engaging in intimidation and dominance displays in order to control females
I have no data, so take it or leave it as suits you. Either way, that's 70% of males with transgender identities that I don't want anywhere near a female restroom.