SORRY KATE, thought that was OK but bow to your enmodulation. x
1) Yes, same receptors are involved afaik but others will know more about this
2) It depends what you mean by high dose. I think that etiz gives me less compulsion to redose than diaz. What Acidtek says about being more responsible with etizolam rings true with me although I couldn't possibly explain why.
3) Shitipedia says that etiz has 'six times the anxiolytic effect' of diaz but I haven't seen anything to back that up and that's not how it feels subjectively (and how this could be measured is beyond me). Subjectively, onset seems about the same, half life / duration less. Euphoria / mood lift seems a bit greater. I believe that the half life is much much shorter than diaz, I think it may be in single figures. I guess that this could potentially cause quite significant problems if someone acclimatised to diaz (ok, addicted) was using etiz as a straight pill-for-pill replacement. I don't think it works as well as a muscle relaxant and I think that I get more of a feeling of glowy contentedness from diaz but these are just suspicions of my own and seeing as these drugs both play havoc with my memory in the right doses that's all they can be.
3b) At least one person I know with long term benzo tolerance has reported not getting much out of etiz (although they only tried it once).