212man is right, of course. That should be obvious.
Unless you operate within a very limited area, where all operators can agree to deconflict with each other on an arbitrary (e.g. 950) pressure setting (e.g. it has been done in the North Sea) - then QNE is the only solution. But will / can ATC provide it? That is the question.
And, equally obviously, that only takes care of other traffic. Doesn't help with terrain clearance en route.