It got down to 29 degrees last week. I used one layer of Agribon-19 to cover tomatoes, ground cherries and eggplant, and two layers to cover peppers (just because I had it on hand). I left cape gooseberries and potatoes uncovered because the former is a useless crop here and the latter was almost done.

The Results:
All plants covered with single layer agribon were killed halfway to the ground
Peppers with double layer agribon had their tops burned; otherwise fine.
Potatoes mostly killed.

Cape gooseberries are totally fine, except for light burn on leaf tips.

It looks like they are the most frost-hardy of common nightshade crops.