In reply to sean1: I'm sure either of those are good; I've found I tend to fit Patagonia much better than I do RAB, so you body shape might determine the best one.
If you want to save money, consider the Uniqlo ultralight down jackets. I got the non-hooded one for 50 or 60 quid at Christmas and it is amazingly light. The hooded ones look just like the the Pata and RAB versions, I might get a hooded one sized to go over my current one for next winter.
The uniqlo ones have a higher quality of down in them it seems to the other cheaper micro baffled jackets you seen in other big sports chains, so they pack down to nothing and you don't get feathers pushing through like happens with cheaper down/feather mixes.