I have a Cunningham gelding who turned 4 this month. He is quite tall but not thick (and I don’t think he’s going to end up that way). He was measured in October at 17 1/2 inches and I think he has grown since then. Dam is tall though.
He is the SWEETEST boy, so laid back. He was very lightly started in the fall and then has been ridden sporadically over the winter (basically off). Starting to get back into it and I can not ride him for a week and hop on w/o any lunging or issues. He goes out on trail by himself or in a group, not herd-bound or distracted by stuff going on around him. No spook, buck or rear. He has never done anything naughty at all. (so far!! 
He has been free jumped at the Young Horse Show series shows and could easily be a very nice hunter. But I am going to piddle in lower level eventing and dressage and just have fun.
I met Cunningham in person last year and yes, his neck is MASSIVE. Such a gentleman, so polite and well behaved. The owner is wonderful, she took time out of her busy day to show him to me and chit chat about him.