Hi Adam,
Nice job on the Mamey. Those are very cold sensitive trees. I have heard that one guy got a Mamey to fruit in Sarasota area, and it was the Viejo cultivar. I spoke with Noris Ledesma of Fairchild, and she said that in her opinion, Viejo is no less cold sensitive than the other varieties.
It'd be really cool if you could get it to fruit!!!
Brad