I'm away right now, so I'm having to keep these short. If I need to, I'll try to add more when I'm back. But for now, a few brief comments:
You mention late-developing speech. The VCI on the Wechslers is more about expressive than receptive language. I would imagine the odd disparity between VCI and reading reflects the oral language delays. That may (likely will) change in a few years, when his vocabulary and knowledge have received a boost from his reading prowess. And it matches the achievement done closer in time.
The VSI is the kind of visual-motor cluster (similarly PSI, about which more later) which I would expect to be affected by motor planning issues that often manifest early as apraxia, but which should more accurately be classed as dyspraxia, not limited to speech.
FRI is in the gifted range, and the single best measure of overall intelligence.
WMI has multiple reasonable explanations. I would agree that looking into sleep is prudent. However, it is not unusual for apraxia/dyspraxia to be accompanied by poor working memory (relative,in this case). They have difficulty acquiring automaticity. Looks like his auditory memory is better then his visual memory, from the incomplete set of subtest scores.
PSI has a high score and a low score, distinguished by the crossing out task vs the stamp marker (like a bingo marker) task. (Actually, the other way around.). This may also be a dydpraxia/motor coordination thing, as one is easier than the other, from a fine motor standpoint.
His achievement scores appear to be no longer representative of his skills, a year later, based on your classroom reports. His oral language lag was probably interfering with his reading growth, in the past. Plus lack of formal instruction in the vocabulary and written symbolic language of mathematics was likely a factor, as your evaluator said.
