My 2p worth is that some of the posts in this thread need censoring/removing. Getting back to the point of the thread, I wouldn't appeal this as either side. I think the ruling is about right, since the exact layout isn't necessarily clear even after the ace of diamonds switch. However, with the possibility of a 2 card suit in the West hand, it may occur to North to not continue clubs immediately, so there is some possibility of a diamond switch. As to the exact percentages? I think getting it right 50% of the time (as North) may be a bit high, but I'm not convinced that strongly.