As far as I have seen them growing, white sapote is almost marginal here, just about the same as citruses, and we are zone 9. My white sapote survived the arctic blast last year with only leaf burns. It got 20 deg F for about 12 hours, and almost a week of below freezing temperature more than 10 hours each night.
I think the cultivar that I have will survive temperature down to 18 deg F.
Here are samples of white sapote:
white sapote - Google Image Search