DX is really hard to evaluate because it basically has two main aspects: manual dexterity and bodily dexterity. In the real world, few people have high scores in both. Magicians, for instance, have a high manual DX but should not be especially good in football or gymnastics. On the other hand, athletes have high bodily DX, but should not have steadier fingers than the average guy.

Until we can come up with a good way of evaluating DX (maybe by using Basic Move and other derivates of DX?), I can only treat it through the game designer's lens, i.e. use the same score range as for IQ. This is because IQ and DX both have the same cost, and are both widely used for buying skills. According to IQ Reality Check, 99% of people are in between 8 to 12, so we'll assume it's the same with DX.

For very good characters, you can buy (or create!) Advantages or Disadvantages that modify manual or bodily DX. You can also add a few Talents to the mix. This should model pretty realistic characters.