All I know off hand about potassium cyanide is it's what Jim Jones used in the infamous Kool-Aide at Jonestown. It certainly got the job done, as it's one of the most deadly poisons out there, but it is NOT painless. I can't stress that enough. There are people who think cyanide is like peacefully going to sleep, but it isn't. And keep in mind, with many of the painful poisons, I can imagine your SI is going to kick in like a futhermucker after you take it since you're absolutely going to be writhing and frothing in pain. I don't know if this is helpful or not, but if you want to know what a mass cyanide poisoning sounds like - the recording of the Jonestown Massacre is easily findable, I think it's right up on Youtube.