I can't promise profound...
I was an absolutely LOUSY speller as a kid, despite being GT and positively addicted to reading. In the big 5th grade spelling bee, I went out in the first round. No one could believe it, since I was the "smart one" in the class, especially verbally. The teacher actually gave me a second crack at the word because she figured I must have misheard her or something. It was very embarrassing.
To this day, I cannot spell a difficult word unless I can write the word down, and then I often make a mistake the first time. I do SEE the mistake as soon as it is on paper, but I need to use my eyes to catch it. I think I am a visual-verbal person, if there is such a creature, because I'm very visual but not spatial. (I'm beginning to suspect that might be what DS7 is, too, BTW.)
DS7 is very good at sounding words out, but his spelling tends to be phonetic, which is not always correct in the goofy English language. I wouldn't say he's a better speller than average. He does fine, but I don't think he spells things that other kids his age couldn't spell.
I suspect spelling is one of those odd obsessions kids might choose to have, as my son chose cars or Transformers. But NOT choosing spelling as an obsession doesn't necessarily mean a child isn't GT. I suspect the English language is so goofy that a child isn't likely to have a natural talent for spelling--at least not with very advanced words--without some study. But if the child studies spelling, that could indicate GTness.
No evidence, just anecdote...
