Alfalfa fall dormancy

What all exactly does the fall dormancy rating of alfalfa mean and how important is it to plant a variety that has the suggested dormancy for your region? The reason I ask is I have a field that I am planting alfalfa into this spring but I suspect I may have a weed issue in this field so I wanted to plant a roundup ready variety but didn't want to give up the leaf hopper resistance. I looked at the alfalfa variety leaflet and there were only a couple varieties that were both roundup ready and hopper resistant and they were all fall dormancy of 4. Here a fall dormancy of 5-7 is suggested. I have been using a variety with a dormancy of 5 and I have never actually seen it go fully dormant in the winter.....stayed green all winter but doesn't really grow in height. Is it going to hurt anything to plant a variety with a dormancy of 4 here?

Alfalfa fall dormancy