What do you mean by bad weather ?

i use my 987S all year, and drove it in 4 inch deep snow on a few occassions last winter on its Pilot Sport tyres - i did have the benefit of fresh snow, rather than that already broken and compacted by other traffic in my favour. ITs pretty hairy at times - 20mph with the psm light flashing away and not exactly pointing forwards on a perfectly straight bit of road (crabbing along). The cayman would be no better, the 997 maybe a little with the extra rear bias, but wider tyres would probably nullify the advantage.

In heavy rain and sleet there is nothing in the cars.

I had a hard top on my previous 986, and whilst this did cut down some wind noise on the motorway i didn;t feel overall it was worth the hassle of fitting, storing etc.

They are all round cars, the biggest weakness for any of them is the summer tyre technology.