"Gifted" does not have to mean fast.
My son has much the same profile as your son. His WISC score shows him to be PG on the Perceptual Reasoning section and to have an average Processing Speed.
FWIW, my son is definitely NOT OCD or ADD. He's just a deep thinker who processes at the speed of an average 8yo. That doesn't mean yours isn't dealing with some other issue. But it does mean that it is possible to have the profile you're describing and not have other issues. DS8 isn't really even a perfectionist. He's just not gifted in speed.
With my son, I chalk it up to that spiky asynchronous thing that so many gifted kids have in spades. The thing I remind myself regularly is that the odd thing about him is not his speed. That's actually the "normal" part of him, the 8yo part. The odd thing is the fact that he can understand such complicated issues that most "normal" 8yos can't comprehend.
The thing that we have done to accomodate him is to homeschool, since speed does matter in a formal school situation. I suspect we would have a harder time making things work well for him at a school because he needs significantly harder work, but he needs fewer problems and more time to work them out. It would be a challenge for any teacher to make it work. But at home, I am able to work on his speed even as I downplay how much it matters in other areas (much as I would if it were a real LD).
I think you can mention it to the doctor if you think it will help you feel better and if you think the doctor will understand and be supportive. But if the only evidence you have of problems is an average speed score--especially for a perfectionistic kid--then I guess it doesn't seem to me to be a real problem.
Of course, all bets are off if you see other symptoms of OCD or ADD... Trust your gut!
