In reply to UKC Gear: Good review.
It is worth noting that down will last a lot longer than synthetic insulation. Synthetics eventually loose their loft, whereas a high quality down bag, if well looked after, should last a very long time indeed.
Also at 1200 grams the bag is way too heavy for summer alpine climbing.
A sleeping bag with a total weight of 500g should be more than enough. Saying that there are very few summer alpine routes, which require a bivi, that I would bother to take a sleeping bag on.