The Big Kaboom!!!

[Fuelie Fan]

I'm not at all surprised that it was the pistons. Rods actually rarely break of their own accord, usually something else happens first, a bearing seizes or something, then the rod gets thrown out the side of the engine. Your combination was pretty much the THE recipe for popping a piston. Also, plug coloring can't reliably be used to judge mixture. It's a starting point, but not a fine tuning tool.