I had Mike Orlen open up the chokes on an old LC Smith Field Grade several years ago. Prior to doing so I ask the same question as you and I received pretty much the same responses.
What I learned from the process is this: open the right barrel to what ever you want, and I would suggest IC or Skeet but have the left barrel be a little tighter than you think you want. I hunt in nothern Michigan and I think that IC or Skeet is good for the left barrel and IM is perfect for the left barrel.
The important thing to remember is you can never go back and have more choke put in so opt for a little tighter in the left barrel. It can always be opened more later if need be.
