Thanks for the input aeh, I really appreciate it. I hadn't really considered that his fine motor might be actually delayed, I definitely noticed that it is a relative weakness of his compared to his performance in other areas, but I guess it looked normal enough compared to other kindergarten kids. I will have to have a bit of a closer look at how he's going there I think, and whether it warrants further investigation. He definitely has issues with perfectionism so that may be a factor as well.
I have read into symptoms of processing speed deficits today, and I do see some potential symptoms there as well. He's an interesting little thing, a bit of a mystery to me! At the moment he is coping and performing quite well at school, the only issues have been that the academic level is far below what he's capable of/interested in, but I'm a bit nervous about how he'll go into the future.