Thinking of all the hybrid cats I've killed by keeping them outdoors during winter...I'd say a pessimistic estimate would be around a 10% survival rate. The survival rate bumps up to around 25% - 50% depending on how much laelia the parents have in them.
Here's a couple of websites that might be helpful...
Outdoor Growing List for Manly Warringah area of Sydney (occasionally down to 32F)
Outdoor Cattleya List for Kerang, Australia (occasionally down to 23F)
I suggest going for it... remember what Harry Phillips said? Something like, the more orchids you kill the better you'll be at growing orchids. Hmmm, or perhaps it was more along the lines of, the difference between a novice orchid grower and an experienced orchid grower is that a novice has killed dozens of orchids while an experienced grower has killed thousands. Or something like that.
Finally finished completing my new shade shelter and setting up the misting system. I'm pretty happy with the misting system and plan on putting up some photos when I get back from Texas. Let me know if you want to come over to see the misting system in action.