Titanopsis calcarea 'Kimberley Form'
Titanopsis calcarea also known as Hardy Living Stone is very cold hardy if proper drainage is given. Have had these take -10F where the winters were really dry. But this plant is grown more as an indoor plant. Plants only reach 5" across and 2" tall. The seed for this plant came from Kimberly South Africa and is the most cold hardy clone we grow.
These South African Succulents can be grown in containers, on a window, in a greenhouse or anywhere you can observe the plant. A favorite of mine that goes well with the white flowering form and Aloinopsis.
I do not guarantee these in a zone 5/6/7 because everyones growing conditions are different but this would be a good trial plant to grow in your cold outdoor garden.