Dear Dvenman,
Nearly always have the top down, exceptions are high winds and blizzards above 1000 m and less than 30 mph! More seriously, top down motoring is very comfortable under most conditions in a 981. We find we only need drive top up when its very windy or in slow moving traffic in the rain or snow - above about 30 mph it just goes over the top.
Took delivery last January with Continental winter tyres fitted to standard 19" S wheels. Good traction under all conditions (cold, wet, snow & ice) - most will find them very good in the cold wet conditions that prevail in most of the UK. Living where we do, you can travel from temperate maritime to sub-arctic conditions in less than a 1 h drive. For us they are essential and we have them on all our vehicles from about the end of October to the end of March.
Note added- We have the excellent PTV with LSD option and in combination with the winter tyres we remain largely spin free but without the loss of traction you get when PSM acts alone. Hill-climbing ability is excellent. Overall the main limitation is the depth of the fresh snow, ca 8".
Winter wheels & tyres are changed over free for their lifetime by Porsche garage. Ran them well into April this year since we enjoyed late snows and low temps with the late onset of Spring. Only other essential was winter screen wash - recommend LIDL German proprietary 5 L winter wash additive (buy early it soon sells out).
The heated seats are very good but we only use them mostly on their lowest setting at the start of the journey, they might come on again as the conditions get colder but when its really cold we prefer to adjust our clothing. The point is, whilst they are very desirable, they are not essential for top down motoring (ie heated seats).
For headgear I usually wear the modern, universally available, ''Polartec fabric head comforts', my wife like the 'Buffs' tubes worn in the balaclava style. This winter I'll be trying out a snug fitting Russian style shooters hat with ear flaps. Either way it's essential that the headgear is comfortable, cosy, stays on (it's more blustery in the cooler months) and can be dynamically adjusted to cover your ears. Sartorial elegance is desirable but not essential!
Windproof fleece/fleece lined coats are essential. I use a Schoffel Rutland Polartec fleece (Gortex windstopper lining) when its very cold and a 'Rohan Kombi' jacket when it's just above freezing. My wife mostly wears a 'Musto Performance Snug' and we both vary the sub-layers with the full or partially zipped Rohan microgrid stowaway tops. Comfort fit is essential. Don't forget the winter trousers, the chino-style Rohan winter route trousers for men (zip free rear pockets - no seat damage) and for ladies the Rohan striders are good when its very cold. Passengers can also benefit from a some traditional upper leg protection in the form of a wide fleecy scarf draped over their thighs when the temperatures really drop (the point of this is that it can be easily adjusted to suit the circumstances ie dynamic layering). For cosy feet I prefer 'Scarpa' approach lace up climbing shoes. They are not the commonly available boot-like trainers but are lightweight, narrow and with thin grippy soles and will accommodate lightweight merino wool socks of the 'Smartwool' variety without loss of foot sensitivity (look in specialist climbing outlets under approach shoes).
Finally gloves! I use Polartec gloves (currently good value Black Diamond) of different weights depending on the windchill (weight depends on the 'fleeciness' of the lining). The gloves are smooth with a snug fit, not bulky and sometimes referred to as lining gloves in the specialist outlets. It is essential that they either have leather lined palms or have the more modern sticky artificial surface treatments, either way they help you grip the wheel! Options are the electro-conductive treatments of the fingertips so that you can operate touch sensitive screens etc. My wife has the more modern (and expensive) Mountain Equipment lightweight variants with silvered thumb and finger tips with a natty mountain profile sticky motive that form the grippy surfaces on the palm and finger faces. She finds them excellent under all conditions.
hope that helps
FBR