My worry about a grade skip, frankly, would be precisely the lower scores in the working memory and processing speeds.
When a younger child is placed with older kids, differences in those areas are magnified. Many teachers expect GT kids--and especially GT kids who are grade-skipped!--to be fast and to have "photographic memories." If he is not above-average in those areas, I would worry that he might run into difficulties.
This is one of the big reasons we didn't push to grade-skip DS7, frankly, He had above-average-but-not-GT WMI and PSI, and given that his at-grade-level teachers always wanted to pick at his slow speed for getting things done, I just wasn't sure he could succeed and be happy if grade-skipped.
Not that what's right for us is right for you or anyone else, but it's something we considered when facing a similar situation.
