The "limitations" often depend on things like the birds, the habitat, hunting pressure etc as much as (or more than) geography. I don't think you need any more choke for a grouse or woodcock in Upper Michigan than you do in Maine. And especially early in the season, you don't need any either place--at least not in a 20ga or larger. I hunted wild pheasants for several years with a 16 and a couple 12's choked .005 in the R barrel, which is not a lot and certainly less than most people would suggest. But over good pointing dogs, using the right loads (between an ounce and 1 1/16 of 7's or Brit 6's), the combination was absolutely deadly.
