Trying to work out if you should kill 5-Torg in High on Life? You only have a single opportunity to slay the cloned sister of 9-Torg, and it's shortly after the first boss fight in the game. It's a missable moment, but as it turns out, it's one you may wish to not bother doing.
There's a similar moment a few minutes later in the stab Gene with the knife. However, that moment is different because you can get a secret achievement for being a bit of a dick. This choice, on the other hand, is one of the more disappointing ones.
The short answer is that it doesn't matter if you decide to try and kill 5-Torg in High on Life. Yes, you will see a health bar appear as if she is a boss when you first hit her. However, as she is tied up, she can't fight back. In addition, killing her in cold blood does absolutely nothing for you, so if you end up murdering her, you'll have no reward like an achievement to show for it. It's actually quite underwhelming that you get diddly squat for being such a dastardly villain, especially when the other choice matters a bit more.
So no, there's no reason why you should kill 5-Torg in High on Life. That isn't to say that you can't get a best PC games of the year.