When double impatiens first came out many years ago I was given one by a lady who had a rare plant nursery, and I carried it with me through many moves and for a lot of years. I finally lost it by being too relaxed about it when I moved here where I should have been able to keep it easily. Since then I have had several different colors and all have done well with a little winter protection in the way of mulch and sometimes covering for more cold. Can't imagine why you would have a problem in z10 with either double or single if you keep them moist and protected from Santa Ana winds and brush fires.

San Francisco is a bit harsher then most of Southern CA, which is probably why the singles did not make it. The singles tended to be smaller in size, and the doubles make a larger more robust bush. I will post a photo in the gallery.

Bad news they both died, this winter. I thought one was going to make it up until Febuary. I planted new guinea types this year, maybe better luck?