What's the differences between these two stances?

Kill shot by name would seem to imply a finishing kill swing. But that's not a ton of information.

Berserker, I can imagine and have a better idea (high endurance use, hit hard, little care for self injury, etc). Of course I have no idea what applies to this game per say.

Anyway, if a beta tester would respond with any additional information, I'd love to hear it (even if it's just theory).