Thought that you guys would like to see how long my horse's mane is now. Last year, in August 2006 I was forced to roach her mane. Now it is finally long and I have been using MTG ever since. Her mane ended up growing nearly 17 inches in one year in a few places, I guess MTG does help... And I just bought my second bottle a few weeks ago!!
I googled for the answer to this and found this info from a "real person" (not an advertisement) on another website. Hope this gives you some real world info to maybe judge the growth on.
To me I would guess you'd have half that amount of mane by spring, if you roached it now. I would also guess that banding it as soon as it's long enough will give you a "polished" looking mane.
Hope I helped.