I would tend to agree that 10% is approaching the maximum for crystal malt but there are some good beers out there that use a bit more than that. I was looking at Jamil's Dopplebock recipe the other day and he uses 2lbs of Caramunich in a 6 gallon batch. That beer won gold at NHC...just sayin'.
Jamil would admit that the recipe that wins competition often isn't the recipe that makes the beer closest to style. You need to play to the judges expectations, which sometimes means making a parody of the style. So a beer like this or a Scottish Ale might be made with a lot of crystal malt for competition, while a real example might contain little to none.