I took a taxi in Finland a few years ago when there was 2 feet of snow in the fields and a good 4-5" compacted snow on the roads. Temperatures were about -20°. The driver was taking bends at unbelievable speed with no problem (it was an E Class MB) and when I asked him how he did it, he said it was 10% skill and 90% winter tyres. I don't know if they are worth investing in in 'warmer' climes, but I have no doubt at all about their effectiveness.