In reply to yoyoalpine:
I'd ditched the spare down and waterproof. If you need either of these, then it's probably not the weather to be anywhere near there.
Fleece jacket of some type, but not the thickest. Wind/water proof jacket. I'd probably start with 3 layers on the upper body when setting off very early doors. Then at first light, ditch layer when I stop to lose head torch and put on glasses, drink and suncream all at the same time. Job done.
I'd also only pick jackets that have pit venting. As if you can lose some heat without having to stop and lose or swap layers, that's time saved.