As you well know, on a wall you’re probably just about as exsposed as a human being can be, and in a storm you’re just as much in the shit as someone who’s fallen overboard, and the ship has sailed away. Strangely when it’s cold, and below freezing, things get much easier, for example 14 days on the Troll at -20 was way easier than 10 days on the troll at +5. Clothing can deal with wind and sun, but water is the killer. Someone floating even in a warm sea will die of hypothermia, and so someone drenched in cold water and slush in a wind storm really needs the best kit they can get. The best kit to deal with water is still fibre pile, either plain pile (old school!) or shelled pile (Montane, Brenig or Buffalo). We used pile suits this year on the Eiger (were it went from freezing cold, to piss wet through in a few hours) and Ross and Neil were really impressed (by the time we’d post holed down to the train station we were absolutely soaked, but totally warm).
Also on a wall you tend not to be going super fast, and just need a lot of insulation when static, and doubly so when it gets bad.
I’d probably use the following system:
Long base layers (good for sun and keeping mosquitoes off)
Fibre Pile top and bottoms
Shell top and bottoms
Heavy duty synthetic belay jacket (that fits over the lot)
Two medium weight synthetic sleeping bags and bivy bag
Don’t forget gloves, mitts, gaiters (to keep rain out of your boots) and balaclava.
Keep everything in dry bags, but have a system that is totally solid wet or dry.
If you’re realy worried about staying warm, then get a pile one piece suit from Brenig, which costs about £50 (you can get through the leg zippers added for ‘lady toilet time’) or use Montane or Buffalo kit.
I always think that on any big wall you need to have the same kit as you’d have for doing a big wall on the Jorasses in winter, and typically that approach works well. Once you’re up there, and the rain starts to fall, any doubts will soon prove well founded, plus having a bomber system means you remove just one more reason for bailing!