I use 85gr. of T7, and with a 250gr. xtp killed a deer at about 150-60yds. two years ago. From everything I've read and figured, I'm getting around 1700-1800fps with a 250gr. bullet(closer to the higher), and that is using 85gr. I would say that you could get down to 70ish grains, and as long as you place your shots you would be good within a 100yd. or a bit further.
~Amos