I used to use them for everything in my 30-06s. I took several elk using Federal Premium 150 grain Sierra Game Kings until one day it took four shots in the lungs at 30 yards to down a cow elk. So I switched to Federal Premium High Energy 180 grain Nosler Partitions and have taken a bunch more elk using those, with no problems.
I still use 150 grain Game Kings for deer and smaller game. I just got back from an antelope hunt in Wyoming and got two bucks, both one-shot kills, using them.
They are very accurate and I love to use them for practice because I get such small groups. Pumps my ego.
Sierra Game Kings are a great bullet when used within their design parameters.
KC