A good bullet should punch straight through at 150 yds. A REALLY good bullet should punch through both shoulders at that distance.
I shoot 250gr Hornady XTPs over 1300fps and 300gr XTPs near 1200fps from a 6" barrelled revolver.
From a 20" barrel, at 150yds, the 300gr should still be well over 1000fps.
I am certianly no expert on ballistics, but I have significant experience deer hunting(killing). I believe that if you can hit it correctly at 150yds with a very warm .45 Colt load with a good bullet, you can kill it. The important thing is whether you can hit the vitals.