I suspect you have a greenhouse.. But, I also suspect you've grown a lot of the Mexican cultivators in your 8b zone.. I'm beginning to think that a lot of the Mexican cultivators have random seedling mothers mixed in. Like, someone may have grown out a seed from Joey and then called it Joey and passed it around and eventually it got sold?? do you think that might be the case? I know taste is different for different people, but I'm seeing very drastic differences of opinions on the taste of Mexican varieties. And after reading the very long post on avos 24/7 I see a couple mentions of variability in individuals of the same variety ?? Including recently from you. ??
I think environmental differences account for a big part of the variation, but also I think people often will say that two varieties are "the same" based on visual similarity of the fruit, rather than actual knowledge they are the same, as I suspect is the case with Fantastic & Del Rio.
Mexican avocados do poorly in most of Florida due to the thin skins allowing them to rot or get damaged more easily. Some people may also leave them on the tree too long, when their consistency and flavor begin to deteriorate.
There may also be an epidemic of mislabeled trees from some online nurseries (e.g., Fast Growing Trees sent me two trees that were definitely not Poncho or Brazos Belle, they weren't even Mexican avocados).
As far as flavor, Mexicola is a very good (very small) avocado. It may not be as hardy as some others, but it should be available from most CA nurseries, and it's worth a try. Duke is also good, with the tree in Oroville publicly accessible if you can't find anyone selling them. I might have scions next winter, if you want it then.
And yes, I have a greenhouse, but have also been planting out many seedlings and grafted trees to test the claims of hardiness. The project is still in the early years, though, the greenhouse trees are only 2-3 years in the ground at the oldest. I'm hoping next year they will be large enough to start producing seeds for the project.