Duane and Jay, thanks for the advice. I am thinking then if I get a cocoon with hood that will be enough extra insulation with a Ghost at night. I still want another head layer, mainly for on cold mornings (I like to start at the crack of dawn but its often still around freezing point) when I start off. I usually start off in just my hiking shirt, polypropylene gloves (thinking of moving to possum down though) and a polartec 200 beanie. I get cold hands so covering them up, plus my head gives me enough warmth to start off with, but those layers are easily removed and stashed in a pocket once I get warm. I think the polartec 200 beanie is a bit too warm if that is its main use, so I might get a the lighter Icebreaker (NZ brand) merino wool balaklava. Should be versatile enough.
The other option I was thinking of was trying to make a Kennebec or Kinsman Pullover from thru-hiker.com, and then going for perhaps a light balaklava AND a possum down beanie. The kinsman in M weighs in at about 7oz, which is a weight saving on the cocoon with pullover (9.5), the extra 2.5ounces easily covers the 1.85 of the possum down beanie. And I will save a bit of money (skint student).
Actually Duane, the only place I have noticed in South Australia to get possum down clothing is here at BPL on the net! Crazy, I would have to buy something from across the Tasman via the US. Possums are an introduced pest species in NZ, but in many parts of Australia are threatened (so we don't get that kind of stuff here).