I couldn't find any real live KU31 despite online adverts so I put a pair of KU39 (235/45/17 97Y) on my fronts a thousand or so miles ago. They were a little noisier than I expected at first but have now quietened down very nicely indeed. The tread pattern is suspiciously like the Conti SC5, with a couple of humongous wide grooves right around the circumference bordered by nearly slick areas. I suspect they were aiming for a similar end result: quiet and comfortable, good grip under all conditions at the expense of just average tread wear. UTQG of 280 AA/A tends to confirm this, insofar as it means anything at all.
They have refused to let go under normal (moderate) driving. Yesterday, I was deliberately trying to provoke them on a 60 mile drive over Sussex twisties in light drizzle. It was the Yokohamas on the rear that came unstuck every time, straight line braking and on bends, and despite having a bit of weight in the boot. I think I would have to put the Kumhos on the rear to give you any decent information on how they behave on the edge, and I can't be harrised to do that just now.
Other reviews here FWIW:
http://www.tyrereviews.co.uk/Tyre/Kumho/Ecsta-KU39.htmOverall I am very impressed with them - quiet, comfortable and no nasty surprises. I will be buying another pair when the rear Yokos shuffle off.