That last bit is exactly the reason why I'm afraid of going out in the GTR when its freezing/snowing.I have a second set of OEM wheels with some Blizzaks I got from Tire Rack on them. This will be the third winter on them. Overall:
1. Grip in the dry (even at mild sub-zero temperatures) is inferior to both Bridgestones and Dunlops, and also MPSS which I currently have on.
2. Grip in the wet is far better than the Dunlops, and better than the Bridgestones. Standing water no longer causes buttock-clenching on motorways and A-roads. I'm not sure how they will compare to the MPSS, which are better than the OEM tyres in the wet, but since my Blizzaks are OEM sizes and my MPSSs are 285/295 front/rear it's not quite a like-for-like test anyway.
3. If there's any slush or snow, the difference is night and day.
I've found that I try to delay the change to my winter wheels, since in normal conditions over an average UK winter the compromise on winter rubber is significant. If I had space to keep another car I would probably spend the £2500 a second set of wheels and tyres costs on a cheap 4 wheel drive winter runabout, but since I don't and I need to be able to drive around for work The GT-R got some new boots.
I think the main danger if conditions get bad are the plonkers driving 10 year old non-ABS equipped sheds over ice on bald summer tyres 20m from your back bumper. My improved stopping distance then just helps them remodel my rear bodywork more effectively...