The synthetic sleeping bag has been replaced by a Mountain Equipment Xero 350 down bag. This weighs in at about 750 grams, and also is about 5C cooler (+20C to -5C). This should be OK as I found the previous bag a little on the warm side.
My only concern is that down's insulating properties reduce dramatically if it gets wet, which brings me onto the Rab Ultra bivvy. On the plus side, it is incredibly light and packs down really small, but it feels rather flimsy and I just hope it's as moisture and condensation proof as my old heavyweight bivvy is!
My pack is now down 3.5 kilos to 11.5 kilos (25lbs), excluding water. I'm tempted to ditch the stove, pan and just take snack bars, which would probably get me down to around 10 kilo, but that feels like a sacrifice too far at the moment.
OK, that's it for now I've bored you to death over my weight issues (some would say I could save more weight by not going to the pub so much).