Thanks for all your comments. I have read them throughout the day and been thinking about this more.

Grinity, I think I overstated when I said that he is moving constantly (it just feels that way! lol). He is capable of sitting quietly, at least to the degree that I would expect a kid his age to be able to. I don't know that the funeral is a good example, because he would be fascinated by that ritual and also possibly very emotional due to his emotional sensitivities, but I get what you are saying. It is just sometimes that he seems to get physically riled up and we are still trying to figure out the pattern to that. And, like Deonne's son, he requires a lot of physical activity throughout the day and plays lots of sports.

However, his 2nd grade teacher says he is doing great behavior wise so far (fingers crossed), although he had a rough time in 1st and ended up switching classrooms. I was being told that the problem was with him (thinly veiled ADHD suggestions), yet when he switched to the other classroom, all the acting out stopped and he had virtually no behavior problems after that.

While I never received a decent answer from the school about what was going on in that classroom (all focus was on what's wrong with him rather than an evaluation of the classroom environment), it was reading about OEs where I really had my aha moment. To me, thinking about it that way made some things about him that seemed inexplicable finally make sense. I think that there must have been something about that first classroom that just caused a sensory overload for him. He told me it was too noisy and made his head hurt. I thought, at the time, that he was being dramatic, but after reading about OEs, I considered the possibility that perhaps that is really what happened to him.
It's interesting that you use the sensory OE and restaurant smells as an example. When he was a toddler, we would occasionally go to a breakfast buffet on the weekend. We had to stop going because he would throw up EVERY TIME! And before he had even eaten anything. At the time, I was completely mystified and thought at first that he was doing it on purpose, but quickly realized he was not. Recently, we went to a similar restaurant and now that he is older he was able to verbalize that the smells made him feel sick to his stomach (thankfully no vomiting!) I feel like learning about OEs helps me better understand how he sees the world. I still can't control it for him, but I am hoping that I will be able to help him develop strategies for dealing with it. And of course these issues are also complicated by his motor skill issues that we are working on in OT.

As for ADHD, it does seem to become very complicated with giftedness, doesn't it? I mean, there are limits to anyone's attention to something that is boring for them, and I would guess that there is some level of tolerance that one would expect from non-ADHD kids that ADHD kids are compared to. However, gifted kids are likely to be more frequently confronted with "boring" activities so even if they are reacting at the same level as a ND kid, they might appear to have a lower tolerance. Does that make sense?

Anyways, I guess I still haven't answered my own question for myself, but this conversation has been really helpful. Aculady, I like your distinction, I will have to think on that some more as well.