Vertical Ridge Augmentation

Neil, a dentist, asks us:

I was wondering what the general surgical opinion was about attempting vertical ridge augmentation, when more than 4mm height is desired.

The literature appears to state that about 5mm is the
average gain using either distraction osteogenesis, sandwich osteotomy
or a titanium reinforced membrane with implants (i.e. Simion).
I would appreciate your thoughts about any of these techniques, or others that have worked well in your hands. Thanks.