115gr Nosler Partition is a great deer bullet. The 120 is built a little tougher than the 115 for those folks who may want to use the caliber for elk hunting.

The Partition is not NECESSARY to kill a deer. I use 117 Sierra Gamekings for deer and it does a great job as well.
If I am going into an area to hunt for large trophy bucks I always load up the Partitions for the extra margin of confidence they give me. The Partitions just work and I don' t have to give a second thought as to whether the bullet will do its job when using them.
I use them in my .300 win mag as well for hunting bear and elk. Never had one fail to do the job. They seem to have the perfect mix of expansion vs. penetration.