Re: Selecting mid pos. on Dual HBs
All of them. Unless you have foil splits going on. The middle sound is good for rhythm, or setting the neck pickup on full with the tone on 0. That way, if you are cranking on the bridge full up, just moving it to the middle position will give you a very good woman tone instantly.
Jimmy Page had enormous success with both pickups in the middle. Watch him on "Song remains the Same" DVD. He does have coil split, but IMHO he doesn't seem to use it much on songs with jams like the middle fast break on "Dazed" or Bring it on Home".
LIt' good to try one pu'p higher and the other lower, regardless of which ones you try, you'll find a lot of variation there.
You can get a great rhythm sound on the neck very low, say 1 or 2, and the bridge on 10, play rhythm with both set that way and boom, go to bridge on solo level without having to reset anything. Really no limits, but coil spits is something I think is a great idea, if the coil you choose is the louder of the 2 coils in the humbucker.
2 cents
SJB