I don’t own a “pipe snapper” to cut cast iron. So my favorite tool for that nasty job is a grinder equipped with a diamond blade. In tight spaces where my grinder won’t go, I’ve always used a reciprocating saw and metal-cutting or carbide-grit blade. That works, but not very quickly. And cast iron destroys blades fast; I’d go through two or three blades cutting a 4-in. pipe.