I'm going the other way (M2F), but I went to a session at the Phila. conference on transition and singing. The presenter didn't show (a frequent problem this year), but there were something like 50-100 people who came to the session, most of them F2Ms, many of them trained singers.
The main thing they kept saying was: during transition, i.e., as the T starts to take effect, you have to keep your vocal training up. Apparently it makes a big difference in your ability to sing once T has done all it's going to do to your voice.
(Unfortunately, taking E and suppressing T doesn't change your voice back. I'd love to sing soprano, or even to have a proper alto vocal quality. Oh, well, at least I'm a tenor and not a bass.)