summer tires-- continental contact sport 2 give much better wet traction and ride quality than p zero's. i generally prefer michelin tires but they don't make tires big enough to fit on the rear wheels of the c4s or turbo.
winter tires--pirelli winter 210's purchased last wk have been adequate in snow--i think it's tough to get snow traction with such wide tires. on another car i found blizzacks to be poor on dry roads--the 210's are pretty good in the dry.
tires are a tough topic because all choices entail compromise.