This species has such an enormous natural range, all the way from Mexico to Argentina, that it varies considerably in its appearance, as well as its hardiness which to my knowledge remains untested.  It does sound very promising, as anything that grows in Argentina must tolerate some frost; and also that it would be adaptable enough to span over such a huge area.  Most plants are about the size as D. antarctica, or a little smaller; and many have rather yellowish stipe-hairs as opposed to the red-brown of D. antarctica.  However the variety D. sellowiana var. gigantea (which is often just referred to as D. gigantea), which is found in Mexico, can form quite a massive plant with suckers arising from the base and lower trunk.

An English nursery has rated this species to 20°F, but I do not think this figure can be relied upon for all plants of this species; the tropical ones being less hardy and the most southerly ones perhaps more so.