My DS8 loves to read reference books and encyclopedia-type books. I have read reviews of both the Kingfisher and Usborne books, and I'm trying to decide which would be a better fit for him. We have looked at the Usborne Encyclopedia of World History at our library, and he really likes the format of text and pictures. He says that the pictures help him understand the material better. From what I have read, it seems that the Usborne is better for the lower elementary grades, and the Kingfisher for the upper. He reads/comprehends at least at a six grade level (assessed before summer) and over the summer has started reading some adult books, so I would like to get something that is appropriate and somewhat challenging. Therefore I was leaning toward the Kingfisher. For those who have experience with the Kingfisher, do they have the same type of labeled photos as the Usborne? Any recommendations on which would be better?

Kingfisher History Encyclopedia
Kingfisher Illustrated History of the World
Usborne Encyclopedia of World History