I think that the basis for dysgraphia can be complicated and could affect more than the PRI. I'm thinking that things like block design, picture concepts and matrix reasoning could also be affected.

Sometimes gifted kids have "stealth dyslexia" which has more impact on their writing than on their reading skills. They are using other skills to compensate when reading. They may still have weaknesses in visual perception, however.

Read here for more information: http://eideneurolearningblog.blogspot.com/2005/09/stealth-dyslexia-when-writing-is.html