I asked about this a little while ago and got some good advice. I eventually took it all down to 10 inches or so and it's coming back great, really bushy. Here is a link that might be useful: Pruning Cotinus

I've cut mine back both in December and in the spring and I didn't see much difference. The December prune followed a lot of storm damage. Actually i've taken to giving them a pretty good hair cut in May too so that they are bushier with more flowers. Being as far north as Z5, I doubt they will break dormancy if you prune them back now.

dad had one that was going on 15 feet.. blocking his driveway.. and cut it 3 inches from the ground.. and without insult to the root system.. within a few years.. it was back to 6 feet .. and ready to be beat back with a stick again ... i call these type of plants ... 'run them over with the truck' type .... being you can run them over.. and they will be back with a vengeance soon enough ... as noted above.. if you think it needs some help go back at it ... a picture would sure help with future suggestions ... ken

What variety of rose is it? A rose of that height doesn't need pruning, and I wouldn't prune any rose at this time of year. In late March/early April (usual guidance is when the forsythia blooms in your area), trim off anything dead and do a light shaping if it needs one. That will be all that you rose needs.