Exhausted,
It is common for gifted kids to have slow processing speed.
The WISC-III specifically states that when a kid has high subtests in some areas and low processing speed, the full IQ score should be interpreted with caution. It may be more appropriate to use the GAI score to measure ability. The GAI omits processing speed and working memory.
ADHD dx in gifted kids should be treated with caution. Some gifted kids have a delay in the maturation of their prefrontal cortex and it makes them look ADHD-ish. It holds the early childhood learning window open longer, but delays the development of their ability to focus or sit still or use good social skills.
Brock and Fernette Eide are the authors of "The Mislabeled Child" which includes information on giftedness and other exceptionalities. They also have a blog at neurolearning.com.
They've written about ADHD/gifted similarities a lot.
You might find some of their writing useful.
http://mislabeledchild.com/http://www.eideneurolearningblog.blogspot.com/
