I too am surprised by how good the PS4 is in the cold. The general rule of thumb is summer tyres are too hard to conform to the road surface below 7 degrees and will lose grip easily. I've found that to be true of other tyres, but I've used the PS4 in -5 temps without any concerns, just have to take it steady as said above.
I will say though, mine are down to 1.6mm on the rear and 2.3mm on the front (rotated just before the snow arrived) and I did have some sketchy over steer moments in the snow, but that's to be expected if you are a knob driving on snow with slicks
If I had full tread, I have no doubt they would be superb (for summers) on snow. But nothing will beat a proper cold weather tyre though.
As far as what to choose, go with the assumption all of the premium brand sports tyres are ny on equal. Just avoid ditch finders and you're golden.
Nothing beats my old Bridgestone RE720 for all round superbness though, brilliant tyres, but were sadly pulled over a decade ago.
