Although we have lost a couple since we first raised them, the large fowl varieties turned out to be more stable and robust on the whole. Crook neck is not caused by a virus or bacteria, but by an injury to the brain. Many crested fowl (including the Silkie) have part of the brain exposed by way of a hole in the skull.
Silkies are highly entertaining, going mad at the afternoon feed time, you have never seen such a tight scrum. Overall they are delightful birds (a good breed for children) with a very noticeable pecking order and despite their looks, very hardy. Large fowl silkies are bigger than the bantam variety, but they still look smaller than other large fowl of other breeds.
It is prudent to house and keep silkies in their own coop and run, away from the more fiesty breeds e.g. Araucanas. This will avoid the real possibility of injury from other birds with a more aggressive behaviour. Silkies are also short sighted, worth bearing in mind if you have mixed flocks.