This thread is great... evokes a lot of thought.
Killing is a fucked up thing to do, it's something that scars your character's life forever (unless a psychopath), even for Withmore standards, unless they've done it over and over and grown desensitized at the act of putting a bullet in someone's head. But it is ultimately up to your discretion when to kill someone. Determine whether them cloning (or not) will be advantageous to you, or if you want to let them live so they can remember who's in charge.
Paraphrasing Slither, it's important to be true to your character, but it's also important to not be a dick. Unless you have a very good IC reason to kill someone, i.e., they robbed you, killed one of your previous clones, killed one of your friends, framed you, plotted against you to fuck you over (most people who do this aren't newbies, so killing them wouldn't be as a big demotivator), it'd be a good idea to consider how to stay true to your badass roots without making the game un-fun to newer players, who realistically wouldn't stand a chance against you in combat. For example, instead of killing them, you could give them a beating, or hand them over to gangers, or make them owe you money, or humiliate them, or ask one of your underlings to beat them up to prove themselves, things that can create more RP than just sending them to the death funnel.
For instance, I've frequently opted to not kill characters who have been at my character's feet, in critical condition, with a gun pointed to their head. Instead, let them go with a few broken bones, a few scars to tell, and a lesson learnt, giving them, the player, a chance to come back, to plot their revenge, to try their luck against me. Their character has been humiliated and brought to the bottom of the barrel, but they ultimately get a chance to remember what happened and act upon it. It's just how I personally approach it, sometimes.
Other times, you just have to kill them, because they've gone too far in pissing you off and it's the only reasonable IC thing to do. For new players that reroll over and over and over I just think it's their fault and they should try a different approach rather than coming straight out of the gates claiming to be the toughest motherfucker in earth... but that's up to them, isn't it?