Most Cold-Hardy Variety of Autumn Olive

I'd like to plant some trees I have no experience with: Autumn Olives.

Are any varieties more cold-hardy than others?
If there is any differences among the various strains, which ones are the most cold-hardy?

I’m in zone 4 central Montana and my experience here is - don’t waste your time and money. Zone 5 Kalispell several varieties were doing pretty good.

Before you plant Autumn Olive, watch some youtube videos on the lengths that people are going through to attempt to control it in wild areas.  After I saw this, I removed mine, as I have no control over the birds that disperse it.  This is from the guy that plants and grows tons of runner bamboo...