I am confused by the Tanner scale because my breasts seemed to cycle *through* the stages more than once - that "mound on a mound" thing happened several times, for example, with it disappearing for months in between, and the breast buds also softened only to firm up and "reappear" more than once - but it's been at least 2 years since I've seen that look, so I think they might be done with those stages for good. I'm not sure I've reached my "final adult size" yet, but they're definitely rounded and a mature shape with the nipples and areolae back to being flush with the surrounding breast.
So I guess it's sort of Tanner 4.9?

Still growing a little bit, but it's clear that at this point the breast tissue development is largely done and it's just a question of layering some final fat. That phase can take a while; it took my wife about 10 years to get through it. Not to mention that for some women, future weight gain will always go to the boobs...
(4.5 years on HRT, 32 years old when I started.)