BlessedMommy,
This pretty much describes my #2. Spelling in isolation is better than spelling in dictation, which is better than spelling in applied, self-created sentences, which is better than spelling in paragraph composition. We are able to have beautiful handwriting at this point, especially when doing dictation, but, just like with spelling, it all falls apart in composition.
Your instinct is right on the money. So much cognition has to be diverted to the physical handwriting process, that there isn't much left for spelling. If you actually want thoughts and ideas to be conveyed, well then handwriting and spelling rather go by the wayside. The only place where I would shade it slightly differently from you is that I'm not sure I would describe it as the brain not wanting to slow down enough to spell correctly. I think it's more that there isn't enough working memory and processing power left to do letter formation AND spelling AND organizing thoughts AND constructing language.
Something similar happens with decoding novel vocabulary. If you have to consciously transform graphemes to phonemes, and then blend them, it doesn't leave much mental energy for understanding the overall text. It's way easier to guess the meaning of the word from context and move on. In a fluent reader, the process of converting graphemes to phonemes, or calling up whole morphemes, runs so smoothly and automatically that it doesn't really use problem-solving-type cognition, which can then be reserved for comprehension.
As long as he attains all levels of phonological awareness skills, and has sufficient opportunity to practice them to automaticity, eventually it is likely that orthographic mapping will become more efficient for him, and decoding will become less of a guessing game. It is possible, btw, that your DS still has some gaps in PA, as knowing the phonemes and being able to blend, segment, and manipulate them are not the same thing.
I would not be surprised if the perfectionism and the spelling/sounding out issues play into each other. He knows he can comprehend and communicate at a much higher level than he can perform the associated basic skills. And that that is not typical. The relative deficits hold him back from strengths, which is understandably quite frustrating. It also often contributes to children doubting their higher abilities, and thus being even more reluctant to expose their weaknesses by struggling through those skills in front of observers.
