I've moved many roses before (usually getting them off of Craigslist/Freecycle or because I planted them wrong) and with older bushes.. yikes! The root system is usually quite extensive, but in a knarly mess. But they're not TOO horribly all over the place. I moved some roses that were over 20 years old and their root balls were about the size of a 10gal bucket and were not deep at all, only about 18-24" deep. But they didn't spread hardly at all, not like a tree. And I've moved many trees, too. I've never heard of cutting the roots off. As far as dividing, I have NO idea. I haven't divided ANYTHING before, which I *really* need to do with some of my salvias!! Definitely prune it before replanting it... that's pretty much with almost every rose I think. And I didn't think that Knockouts got that big. I've seen them about 3-4' wide, but never that tall. I can take pictures tonight of some of the mother plants I got from Cliff when EuroDesert closed down.. they didn't survive a freak freeze we had in '12. But I have this image here that shows a well developed rootball on a motherplant.
