I only ever got the 'kill everything' limit break once, fighting a few Head Hunters near Mideel. However, the reels stopped turning just after Cloud had counter-attacked and killed the last monster. So, I got the correct combination of reels, but the battle ended at that very instant.

Let's just say that I was less than happy...

I guess that limit break would work against the final opponents, too, since it can defeat the Weapons, which are even stronger.