When I looked it up and saw Zone 6 for the coldest, I started wondering how they got it to live here. I've seen a few sites now list Chicago as Zone 6a, and further away from the lake is 5b, so wonder if it's not just global warming at work and it really can survive in Zone 5 (or what used to be Zone 5). Your variety, Genista 'Bangles', seems much more cold hardy, down to Zone 2. Is it as fragrant as Allgold? I'll have to look into these more!