I like high numbers only if I'm the one dealing it.
Playing Ragnarok Online for a long time made me love/hate high numbers. If you get a 5 digit number you're usually almost dead or dead. *spams pots* On the other hand if you dealt that its good, if it was a player. If it was a high-tier monster you'll need a 7+ digits to kill it.
But that game became even more extremely unbalanced, and the new stuff they added made me give up.
Pretty much starting out from 1 digit numbers, then after maxing your lvl and equipment you can dish a 7+ digit.
I've been playing Grand Knights History for the past 2 weeks. The digits, I've seen, only go up to 3 and even then damage is usually around 100-400+ for my party's average lvl. If my party was higher lvl I'd probably be one-hitted by everyone I fought. My characters' stats are bad for their lvl, so they can't equip better equipment.
I think instant kill should be:
"∞"
There's no way you can survive that damage.
Slime 1 uses Slimey Death.
Arshes receives ∞ damage.
Arshes has fallen.
You've been defeated.
Game over.
But if that single word is too small for you, make it ∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞..etc etc
Just to show the player how large infinity is.