In reply to tingle:
I just bought a Mountain Equipment Titan 425 wr for the same job if it helps.
It's a -2 bag. 425g of down. 1060grams total weight. £120
I would have bought the ME xero350 but way too expensive. I think there is a xero200 for sale on here in the premier ads.
Neoair Xlite is plenty warm enough. They use Xtherms on Everest you know
Use the 150grams you save to carry some protection for it, you'd end up doing the same with the xtherm.
With that said, we bivied at 3200m, I had a mat with a 1.3 Rvalue, a 5degree bag and still used my jacket as a pillow. And I sleep cold.
Post edited at 00:32