Good thread I wish I new the answer since I am still experimenting but was ready to buy a wind cutter and put my own home made sink tips on it. Now I don't know.
What about the Rio Mid Spey was looking at that also but have never cast it.
Our western GL rivers are small in width like yours only a few are wide like the Mo, Big M, St Marys, St Joe, a few of the wisconsin rivers.
80% of my cast must be 60 feet or less and 20% no more 80-90 feet. But these are only if you are fishing one of the larger rivers.
Let me know when you figure it out.
Maybe we need a special spey line for the GL ?