The reason that I go with the one is that I'm doing my winter riding in Calgary, where the riding conditions are 90-95% dry pavement with patches of ice or snow. If I had two studded tires, my rolling friction and noise factor would go waay up, without much apparent benefit. My main goal is to hold a straight line on random ice patches rather than manouvering. I have found that when the conditions are hardpack snow, the riding is very easy.
Thanks for your advice guys, I'm gonna put my nokian on my rim now - I'll update you as to how it went.