Some cultures don't have words for colors beyond 'dark' and 'light', any number above two, or even a written language.
Also, consider disabilities that would affect vision, reading comprehension, concentration, motivation, etc.

I'm not going to argue that every population on earth has equal strength, intelligence or hardiness... but things like culture, language, nutrition, health do have a significant impact on how they score on a test.
As such, I don't believe giving someone a sheet of paper and a pencil is an entirely useful method for pinpointing individuals or mapping races.
It might be more useful to measure brain activity, if one could figure out how exactly the brain works in entirety.

> Raw processing power neglects memory. Long-term helps for obvious reasons, but short-term is necessary as a working space. Some people have more room than the typical 7+-2 items.

You sound like a computer engineer.