First of all, you clearly have done an excellent job with him, based on his achievement scores. (In fact, there is peer-reviewed research that finds that homeschooling parents can have as good academic outcomes with ADHD and LD children as master's level special educators.)
Secondly, whether or not he is diagnosable as having ADHD, medication is not the only treatment. Nor is it necessarily a bad thing. That's a decision that I would encourage families to make holistically, taking into consideration the needs and well-being of both your individual child and your family system. It's also not an either-or decision. The majority of psychostimulants are short-acting; I know many students who take them only during school hours, but not at night, on weekends, or during school breaks. If his attentional dysregulation interferes with his major life functions or happiness, then it becomes a problem. Otherwise, it's just one aspect of who he is. He's also still very young. Given opportunities to learn and be reinforced for skills in managing his attention, his brain has time to develop the neurocognitive skills further.
To your original PSI question: attentional dysregulation is most certainly associated with low processing speed. These are minimally-engaging rote tasks, without particular intrinsic meaning. Sustained attention for them can be quite challenging for ADHD-ish kids. With WJ fluency scores no lower than 107, I would not be particularly concerned about LD, as the inattention could easily explain the PSI. Were Coding and Symbol Search about the same?
