There's a difference between riding on hard pack with a bike, and driving a car over it. I have no idea why you think an experiment with hard-pack snow on automotive roads is in anyway indicative of what works on cycle lanes.
In Reykjavik they used sand at first because pedestrians prefer that but that is pretty dangerous for cycling so they use salt on designated cycling paths and sand everywhere else.
It depends.. salt works down to -18C on cycle paths as long as you maintain it snow free and do not have big puddles of water. Brushing the snow away down to the asphalt is my preferred surface condition for cycling.
Interestingly Oulu bike roads clearing contract states the company doing the snowplowing can do inspections only on bicycles, not cars :)