You will probably be fine with the Sierra. I' m sure a lot of elk are killed with them every year.
Since you are asking the question sounds like you may have some doubts and may want to give the Nosler Partition a try.

Nosler Partitions are boringly consistent, if you use them you don' t have to give another thought as to whether your bullet will work or not.
They just do the job. I use Partitions for elk, deer and bears. I have gotten reliable performance on every animal I have killed with them.