Go here and scroll down a little bit to read what this company says about either using metal or not:
They're pretty clear, so to speak, about what you can and can't expect.
If I were in your position (and I have been) I would build a soffit down to the 7' height, tile the underside of it, and then let them glaze from base to soffit.
That way you can have your cake and eat it too. No frame, no wobble, no worries, and less steam coming out to fog your mirrors:-)
Best of luck!