This whole time I thought he was a cochin. I looked at images and some did come up like him. So you say he's a mix of cochin and something else? I don't have anymore right now, but i'll post later on my free time. I do have this one of my little flock.
Google pics of white sultans. They don't have enough crest though... but too much to be white d'Uccles. Leg color may be another clue. Are they gray? What color are the bottoms of the feet? Also Sultans have five toes but I can't count how many yours have in the picture.