I must agree with you guys. Too many variables. For zone pushers is not just a matter of good calculation and foresight, but also sheer luck.
Citradia the list you imagine would be of incredible usefulness but you can't get one for any plant species. We have to do our best with guesses, myths, urban legends and "i know a guy with an orange tree in his garden! I swear" (And when you go to check it is a trifoliate orange).
What can be done, to narrow the doubts, and honestly i hope people start reporting such stuff more, is reporting the cases when something dies and something else doesn't. For close grown plants this is as good as you can get to get a list from "the most hardy" to the "least hardy" and that list alone would be awesome.
I have started doing this with bananas, but my space is limited, however i find results interesting.