Salvia miltiorrhiza (dan shen) is quite tender for Zone 4. Though, I finally did get it to survive in the garden beds. I'm sure it won't winter over (we'll see). Maybe not the best species for Montana agriculture. Salvia przewalskii (another dan shen) grows very well here.
One trick I'm learning with borderline plants is to cover them heavily with plastic bags of leaves or other DRY mulch over winter. The trick is to keep the soil from freezing and also keep it from getting too wet. This has worked with cannas and Salvia guaranitica for me at zone 6B/7A..
and I'm anxious now to try it on the likes of Hedychium and other z.8 plants...
Oo! Zone 8 has got to be tough! But really, some plants are very adaptable. Keep trying is my motto!