This is actually a *really* complicated question and, with present medical knowledge of the constellation of GABA-A, GABA-B and GABA-C somewhat lacking with respect to alcohol, it may even be impossible to make an equivalency chart even if we reduce it to comparing BZD's to ethyl alcohol with respect to only the GABA-A complex. The GABA-A complex alone has five subreceptors, and each of the great many benzodiazepines exert their effects through varying degrees of activity with regards to each of these 5 units. For example, alprazolam may exert much more of an effect on a1 than does diazepam, which exerts more of an effect on 2 and 3 with comparatively minor activity on 1.
As I understand it, the effects of alcohol are primarily mediated via the GABA-B complex, although I do think ethanol's primary alpha (GABA-A) unit is the fourth.
Here is another great thread,
"Benzodiazepines and GABA-receptors," that explains a lot about the pharmacology of the gamma amino butyric acid system. I *love* GABAergics and from your stated pattern of use (alcohol and benzo's) I'm sure that would be of vital interest to you.
But overall, I don't necessarily believe anyone can construct an answer to your question based on our current understanding of a number of key components involved here. Very, very interesting subject, though, and I'm interested to see what others have to say. This might be more suited for Advanced Drug Discussion but I'll leave that up to the moderators' discretions. Again, cool post.
~ vaya