I bought the valandré Shocking Blue and The bloody mary for a really good price to a friend of mine this summer.
The SB, LaFayette, BM are designed to be able wear down gear underneath. The point is that they are made foremost for UL alpine climbers in the himalaya or Andes. Of course you are supposed to have the body of an alpine climber who are in general pretty slim. After all it's an ultra endurance sport, you can loose 15 000 calories on a summit day (compare with 10000 of a triathlete).
Anyways, if you have the usual north american fit it' may be tight
The lafayette is pretty Large
the SB a little bit less
The BM a little bit less (specially for the legs).
What I can tell you is that the down is distributed unevenly over the bag.
The foot box, head and shoulder is much more massive than the legs. It seems to me pretty logicall since the legs are full of muscle that produce a lot of heat. The foot box is really massive. The SB head too.
I read somewhere that is was a bad idea to wear your down gear or to layer in your sleeping bag. IMO it's a matter of choice and taste. Alpine climbers do it all the time, I know at least 4 guys that used this technic during 3 weeks in the artic circle. They use a 600gr down sleeping bags and a combi to save weight and they were pretty happy (the temp were -25 F). Moreover with large bags you can putt your stuff in to keep them warm. Finally My cousin did it during all his infancy as a scout. So it really is a matter of taste.
In any case I hope to test those bags pretty soon here in Canada and let you know my further impressions and comments.