I have a non-speedy, pretty verbal, highly logical DS8. If memory serves, his PSI was 109, too, though his WMI was only in the 120s, I think. That WMI doesn't help matters either for him, since he works slowly and then can't hold things in his mind as well as he could if his memory were as strong as his ability to reason.
I see the speed issue much as Grinity describes it: as a bottleneck, something that can interfere with his learning and his ability to fit into a classroom. He had one teacher who strongly associated speed with giftedness, and that class was a dismal failure for him. It's one of the reasons I'm not wild about the idea of early college for him and am trying to find ways to keep him challenged but still in high school-and-below for another 8 years, at least. Until he's pretty close to college-aged, I'm not sure how well he'd be able to keep up in college classes.
If he were traditionally schooled, I think the bottleneck might make it quite hard for him to fit in. While he was in public school, one of the biggest complaints that teachers had about him was that he couldn't finish his (easy) work. It was hard to ask for greater challenge if he didn't finish the regular work in a timely fashion!
These days, I find that he can do beginning algebra, but he needs to do it at the speed of an average 8yo, because that's really what he is in terms of speed. It's challenging to strike the right balance even as a homeschooler.
Having directions in writing helps him. Not trying to do so much mental math made our lives easier (though we still do some to strenghten his weaker areas. I just know that it's going to be hard for him and approach it as such.).
I think the biggest thing for me was realizing that he's not dawdling--which used to frustrate me no end!--so much as he's thinking. I stopped getting so frustrated with him and started treating his "dawdling" as an actual need for extra time. That made life much calmer and happpier for both of us.
I know you didn't ask for advice, so forgive me if this post isn't useful to you. As always, feel free to ignore.
I just know how hard it was for us to deal with a slow but deep kid. It doesn't fit the mold at all!
