I've written a blog post discussing the separation of the whitest winged Kumliens Gull from nominate g.glaucoides. I live in Newfoundland where we see huge numbers of wintering Kumliens,so we witness the true diversity possible in this subspecies. Over here the challenge is finding a nominate glaucoides of which we get a couple of adults every year. This could also be interesting for birders on the other side of the Atlantic where Kumliens is the target.
ps: lots of other stuff on there too, feel free to look around.