Thank you, HK! Your feedback was very helpful and reassuring; although my son is not a fast writer, he is an extremely fast reader, which sounds like it will help!
I didn't realize that the placement of the writing varied on the two. My older children-both out of college-took these tests back in the dark ages, before the writing section became the norm.
And it's reassuring to remember that the writing he will do is compared against the "average" college-bound student, not a very gifted college-bound student. Sometimes, when your siblings and friends are all varying degrees of gifted, you lose perspective on what is normal!