Rob,
I'd contact LL Bean directly and talk to one of their product specialists (they are always really helpful). In the past I've seen guidance on their site which indicates buy your normal size but of course personal preference plays a large part. On the plus side we are talking LL Bean so if they don't fit perfectly getting an exchange/refund will be easy.
Brian
"My father was very sure about certain matters pertaining to the universe. To him, all good things - trout as well as eternal salvation - come by grace and grace comes by art and art does not come easy." Norman Maclean, A River Runs Through It