It depends on the species and the origin, but all the species here (unless otherwise stated) are grown in an unheated greenhouse, don't get any additional heat and do much better there than in an heated greenhouse. Many forms need the cold in wintertime to induce flowering, and won't flower if the temperature is not low enough. Especially in a greenhouse, plants can take much more cold than outside, but in general winters in The Netherlands are not cold enough to fear for your plants. Outside, some plants will die at temperatures which poses no problems inside. This will almost always be caused by our wet falls and winters, and not by the temperatures itself.
In summer, Opuntia's can take a lot of heat, and my plants have to survive scorching heat in the summer, when the temperatures in the greenhouse can reach 50-55 °C. But with those temperatures, some will scorch. Naturallly, scorching will not be a problem outside.