Garcinia gummi-gutta (aka "Garcinia cambogia"... very obsolete name) is generally one of the poorer rated species in the genus for eating out of hand. It's only about 3°C hardier than G. mangostana
If cold hardiness is the name of the game, the one to really keep an eye out for is Garcinia esculenta. Anyone ever tried it? It's native to the southeast foothills of the Himalayas at 1300-1700 meters (southwestern border of China). GIS climate data records say that the average (not minimum, but
average) January daily low there is -4,1°C.
I think that might be somewhat of an overestimate (Lijiang records just to the east show that their average January daily low is around freezing, with a record low of -6,1°C), but... it can definitely take the cold
If anyone is looking for finding new species for zone pushing, the Three Parallel Rivers area of China is argued to be the most biodiverse (species per unit area) temperate location on Earth.