I also think the motivation changes for different things. My DS6 was a level 5 when it came to knowing about Transformers, cars, construction equipment, letters and numbers, etc. (depending upon when in his life you were looking). He was a level 4 at other things that were not his then-current obsession. He didn't have the drive to learn everything about everything, but he would have moved heaven and earth to know more about his pet subject.

I believe there's a very fluid line between level 4 and 5, and maybe between 3 and 4 as well.

Kriston