I'm sure he meant -6 and -4 since your post suggests that you're talking about mixing. I even find that a little high, but we're splitting hairs. I get my mixes to peak at about -10. This is for the MIX, not the final master.
If you're doing your own "mastering", as many of us home-recorders do, then you're probably talking about getting it to peak at about -.2, while the average level is around the -12 to -13 mark. This is just my personal way of going about it, so I'm not saying all final "mastered" mixes have to be at those levels. But that's what usually works for me.