Never worked with Osage but I have made several 48" and 46" "D" bows in the Easter styles from ASH, ELM and most of them would draw 25-26 inches consistantly. So I would believe that backed Osage should be up to the task !!!!
It is really important to have that baby bending from one end to the other, so try to resist the temptation to thicken up the grip area more than JUST enough to have the power curve fade into the tips from the center of the bow's length (hope I said that right) but at the same time it still has to bend. As you shoot it in work your way up to the 27" from about 24-25 slowly and keep an eye on the "evenness" of the bend (curve) of the entire bow.
I never thinned out my limb tips too much and I don't know that idea is really necessary...maybe somebody else could give you advice on that part....anyway, mine did not seem to suffer from the tip shape.
Good luck on the bow, go slow and it ought to kick some serious .....butt.