In reply to Newbie-in-London:
I've been up there in early March. I had thin thermals, skinny down jacket and an alpine start jacket (basically an extremely thin windproof layer) on; that was fine. Drying things out could be a pain so synthetic might have its advantages.
Judging by the facebook photos I was in a windcheater (alpine start) and thermal most of the day, from memory the nights got cold, so ensure you've got stuff that you can be comfortable in when not moving.
Bit of a ramble, hope that helps.
Post edited at 19:59