I drive my 986 in the snow, although not as much as I used too, mostly because I now have access to another car. I have never had a problem, but since the 986 has about 4" of clearance, if the road hasn't been plowed or you can't stay in the tracks of other cars you can get stuck if it's too deep (never happened to me). I have driven through about 2-2.5" of unplowed snow, and probably right up to 4" staying the tracks of other cars. It's doable, but I wouldn't call it fun, it's more nerve racking than doing it in a 4WD.
16" rims are best because they are narrower, allowing you to cut instead of plow through the snow, however they won't fit over the larger calipers on the "S" models. I have always used 17" rims with snow tires (search for info on the narrower tires, I run 205 and 235 now). Summer tires are a liability below 40° F.
If you take it slow, don't accelerate or brake like an idiot, and rev match fairly well you won't have an issue. That said, the 986 does just as good as any other car if you hit a patch of ice/black ice, which is to say not well, however I have never had an issue recovering, which is probably due to nearly perfect 50/50 weight distribution of the 986.
