I would have to say that is overwhelming. Miss B gets 7+' & those knockouts get 2.5-3'. The only way I could see that working is if you put trellis up & let the majority of the vine grow in it & let only a stem or 2 grow in the rose. Although I have never seen this but heard of some folks using group 2 clematis as ground cover & still only let a stem or 2 into the rose bush. If I'm not mistaken, most people only pair clematis with climbing roses.

To save yourself the headache in case this happens to you every year, is just move them altogether & replace them with something from the intregrifolia group. Some of those get only 2-3' tall & prune group 3, means that they are cut back every year & grow from new vines. In addition, they bloom pretty much the whole summer.