These are in many ways harder for parents to understand and deal with than the "smarts" are. DS was the king of meltdowns until he was about 6. It's hard to understand how a kid that is so smart and so mature in so many ways can throw the grandaddy of all tantrums. Someone told me once that for every IQ point in excess of the norm, a child has an equally excessive EQ which is why so many of these kids have such a hard time getting a handle on their emotions. I have no idea if this is true or not but it helped me have more patience when my son was on the floor wailing.
DH has a very difficult time dealing with DS7's OEs. He doesn't understand how he can be so intelligent yet so immature. I have to remind him that he's only a child, often. I am going to use the "every IQ point over the norm" next time we discuss it.
Thankfully for us, DS7's tantrums have become less and less, but when he does have one, it can be over the top.