Well after commuting in the light snow today I've decided to put on some different rubber. It simply doesn't make sense to use low tread expensive tyres in this kind of weather so I've ordered some Yokohama Advan Sport 105's. I'll let you all know how it goes. I'll save my expensive semi slicks for the summer.
I read a trustworthy review of the Cup 2 (actually it was a Pistonheads thread and the chap from Michelin who deals with these tyres was posting), apparently they are much better than the original Cup tyre and work OK on the road above 7 degrees C.
Any 'summer' tyre stops working properly below 7 degree C anyway hence why that's the temp at which winter tyres start to work.
The Cup 2 has around 5mm of tread from new so a new/less worn PSS will work better at displacing water.
Mine have been acceptable so far but when the weather is this cold and icy/slushy/snowy I don't expect any non-winter tyre to work too well.