a small bullet precisely striking and then having enough OOMPH to crush/shatter a pelvic bone is not going to be easy to accomplish when you're sweating, have tunnel vision, shaky hands from adrenaline flush, etc...
The center of mass is the way to go. If that fails, I'd go for a headshot over pelvic.
Just my two cents.
There are three things in this life that make me smile ear to ear -- Mastiffs, Magnums, and Merlots. Don't try to take any of them from me.