There are some trans men (as well as trans* people) on iud_divas, and I know one person is just starting on T. If you don't get a whole lot of responses here, you should totally ask there.

My suspicion is that medical science knows basically diddly, but there might be extensive community knowledge among medical professionals who work with transition (as well as the trans* people themselves, obviously!)

Also, activist and writer Julia Serano (http://www.juliaserano.com/) is a biologist by trade: her degree is in molecular biology and biochemistry, and she teaches evo and devo bio. If you can't get good solid medical answers from the internet and your docs, I bet she'd help you out!