Japanese plums with the highest chill hours?

Are there any higher chill hour japanese plums? The ones ive seen would surely bloom in warmer marches and get zapped by late frosts

Good question.

Fedco says that Elephant Heart is Z4… and a good rabbit hole adventure on Google will show results from nurseries from it being low chill to Z3 and everything in between… literally no consensus on nursery descriptions.

Then there is this forum with a good thread on the subject-