Master levels before exporting as audio?

Sup
So im wondering what some of you guys will usualy have your master levels peaking at (on say quite a hard and intended loud peice of techno) before any kind of mastering.
Im just thinking for exporting my final mix down as a wav so it has a good amount of headroom for myself or prefrebly a real mastering engineer to work with for mastering.

Usualy myself I will try and get my mix as loud as possible but im thinking that maybe there is a good amount of head room I should be leaving free.

Any thoughts?
thanks: )

If i'm going to have my buddy master it, I leave it at -6db, because he prefers it that way.

for my live-set clips and loops, it sits at -2db, to give some lee-way to shitty sound-systems.

-6db is standard telly levels, so that the station can adjust it to suit. Gives the most flexibility

As you are talking about enough headroom before mastering, i think also very important is average RMS value and not just peaks.

cheers folks