Mike,
You nailed the description of Sweet Heart--shriveled seed, slightly softer flesh, elastic peel, and ripe with some green on the skin. The pictures I have seen of FZS in Australia look just like Sweet Heart. It definitely is in that family along with Hak Ip (Florida Hak Ip). The the main difference between the two seems to be panicle size and a slight flavor difference. Just as you mentioned, there are often strains of the same variety with slightly different characteristics. It think both of these are strains of FZS based on your comments.