Well I'm not sure how much help it would be for you but here in Florida I am growing malay apples and the seedlings die at like 50-40F but the tree I have in the ground only experiences die back at around 30F.

The rose apple can go a few degrees below freezing, but the malay apple gets very unhappy with frost.

I've heard rumors that Malay Apple is not as cold-hardy as Java Apple (i.e. Wax Jambu).

Java Apple can be grown in Southern California near the coast, but I've only read of Malay Apple growing in Hawaii.

Most people who have compared the two say Java Apple tastes better, but Malay Apple has more colorful magenta colored flowers, whereas the flowers of Java Apple are plain white. Malay Apple can be very ornamental when in bloom. The shape of the flowers are kind of reminiscent of a bottlebrush tree, very exotic looking.