I have some solid aluminum (I think) 6mm bb's. They are heavy sonsofbitches and I ran a few through my APS which used to be shooting just shy of 600 fps with .2s. Never chronied with the metal bb's but they did not pack enough punch to even go through 1 side of an empty water bottle. I'D say stick to heavy bastards or the madbull heavy weights. They work great.
If I was banging all of them, I'd be a manwhore. At the moment, I'm just an opportunist.