Avoman, here's a video by Jerry Satterlee in Texas who grows each of the varieties you mentioned in his yard (
https://www.youtube.com/watch?v=O5rPwipvHBA). He has other videos on youtube as well. Based on his enthusiasm for Poncho, it's probably one of the better-tasting Texas/Mexican varieties. However, Bill Schneider, who grows several of these avocados commercially and only lives 20 miles or so from Mr. Satterlee, told me that Poncho didn't survive the cold at his own place in Devine--so I assume it's not quite as cold hardy as Wilma, Opal, Pryor, and the other types he has trademarked. I grow Wilma in Tucson and have posted about it on this forum in years past, if you want to search the topic.
Shiro, if you "micrograft" a cold-hardy scion as close as possible to the seed of a newly-sprouted rootstock seedling of a somewhat less-cold-hardy variety, you may be able to protect the rootstock from the cold by raising the soil level until the graft union is a couple inches underground. That way the rootstock stays entirely underground, and is never exposed to the colder, above-ground temperatures. And, even if the grafted variety is frozen to the ground, it may resprout from above the graft, preserving the desired variety. Additional "survival-level" protection can be gained by temporarily mounding mulch or soil higher around the trunk when a hard freeze is predicted.
Here's an example of the grafting technique I use ('Day' scion grafted onto'Wilma' seedling). To avoid contaminating the wound, don't raise the soil level until the graft union is completely healed. Another advantage of this type of grafting is that all the stored energy of the seed is channeled into growing the scion and healing the graft: