I'll second what Kreuzfidel said. I had a pretty low voice pre-T, but have only gained maybe an octave on the low end. But then, even after 3 years, my voice is still slowly dropping. One thing I have learned, though, is that you actually have quite a bit of control over where your voice ends up, and some people have to make a conscious effort to avoid the dread "->-bleeped-<- Voice". If your voice doesn't end up where you want it, it might be worth your while to search out a voice coach to help you.