In reply to SteveD:
I got a RAB Quantum 600 a couple of weeks ago and so am yet to sleep in it, but it's roomier than I expected. I'm 5'11" and 38" chest so a little smaller than you but it's a very comfortable size.
The Needlesports website has this to say on the Alpine 400...
"The Alpine 400 contains 400g of down. Length 220cm suitable for someone up to 190cm (6' 2") tall, Internal shoulder width 70cm, Internal hip width 52cm, Internal foot width 41cm, Weight 970g."
The guys on the phone at Needlesports were very helpful by the way.