I think it should make it in zone 10, your orchid cactus make it right? It's a relative. They won't take frost, I've heard that.
We seem to be getting to the end of the pitaya season here, there are less of them in the stores and I haven't seen anyone out selling them from their yards on the street for several weeks. I bought 2 the other day anyway, they looked a little bigger than usual. I opened one and it was really sour, not as refreshing as usual, too tangy. I tossed the rest of it. Perhaps it just wasn't fully ripe. I've heard that they are best when the curling pieces on the outside are turning brown, this one was still brightly colored all over.
It's been cool here the last few weeks, probably 85f in the afternoons but rain later and cool nights. Perhaps that is why, I just haven't been here long enough to be sure.