I don't think I've seen any evidence to suggest that "gifted kids almost always have lower processing and working memory scores." You may hear about a lot of kids with that profile on boards like this one, because discrepancies in scores can lead to bottlenecks that can cause issues for children.

And I may be in the minority on this, but I think that the WISC-IV tests for processing speed and working memory are not the last word on speed and memory skills.