The 45 is plenty for deer sized animals. Actually, in stock form the 909s .45 has more fpe than the DS 50.
With my 909s, I’m getting a good 5 to 6 shots before POI starts dropping significantly.
I’ve looked into the 9mm and from what I can read up, the Fire 901 may be a great pic. Not a repeater, but can accept a wider variety of ammunition.