I am in 5a, in Old Town, Maine. I put in a number of roses last fall, all of which I had been told were hardy to zone 4. Two of them are listed on HMF as zone 6 default: Rockin Robin and Home Run.

Both were treated as were a number of Buck varieties, and got essentially no winter protection aside from planting them where the snow is piled when the driveway is plowed, so they spent the winter in a snow bank. Rockin Robin came out of the snow with growth buds, is growing vigorously and blooming like mad. In vigor of growth, it is similar to the Ballerina which I put in at the same time, and which also is growing and blooming with admirable enthusiasm.

Home Run, on the other hand, whose literature says zone 4, is the only one that did not come out of the winter growing well. I actually had decided that it was dead and was about to dig it out when I saw a tiny leaf coming up from the root. It now has about 4 leaves, all at ground level, and not seem to be going about growing with great enthusiasm. However, it is an own root rose, so I am willing to give it some more time. I would, though, question whether it is really viable in zone 4.

NOTE: 5 May 14
Home Run never grew beyond these very few ground-level leaves which later died. I dug it out.