I drove with them in severe winter conditions on an Audi TT A few years back. I would rate them about equal to the Pirelli Sottozero IIs I currently have on my CS. How is the tread depth? Below 6/32nds any snow tire's performance is dramatically reduced.
The Pirellis have decent snow and ice capabilities, but really shine on cold, dry pavement. We have seen well over a foot of snow here in the past couple of days, and I've had both the GTS and the CS out...the snow is so deep in places that the GTS (with Aerokit Cup) is throwing up the powdery white stuff like a snowplow; the CS is motoring through it just fine.