The width of the space you are planting the clematis in has no bearing on which to chose since the plant will climb onto what ever shrub is nearby. However, using the average heights given on COTW for the two plants, Prince Charles can range from 1.5 to 3 meters (4.92 feet to 9.84 feet) whereas Reiman averages from 1 to 2 meters (3.28 feet to 6.56 feet). Also, remember you can make any clematis more compact and bushier by pinching out growing tips as the plant grows.

Thank you very much for all of your advice. I really appreciate it. Sound like Reiman would be the pick.