mixing to -6db (optimal approach?)

Ever since I started recording, I've recorded tracks to peak at -6db or so.

When everything's mixed the way I like, I wind up with a master bus that's peaking at, say... -3 to -6db or so.

I know a lot of guys say you should have a master bus peaking much lower than this (for mastering purposes).

So - should I aI'm to achieve a stereo mixdown at a lower level by lowering the volume of every track, or by just lowering the volume on the master bus to my target mix peak?

Thanks!