It sounds like a similar profile to my DS7 and it has been a fun ride for us so far. He scored in the 9th percentile for processing speed, in the 60 something %tile for WMI and then 99+ for VCI & PRI. We met with the school and presented the 14 page report to them part way through last year and all his IEP did was focus on accommodations. When I asked about addressing the gifted side of things their response was that they do differentiation so that would take care of that (don't get me started on that one....).
The accommodations have helped a bit. DS really doesn't like writing and is very slow at it so being allowed to have someone scribe for him as somewhat reduced the battles. On the other hand he is still completely bored in some areas. We were really lucky with his science teacher who was pretty good at differentiation and probably the best teacher we've had so far. As a result he didn't completely hate science, got a good mark and wasn't a complete disaster behaviour wise. Math last year was the complete opposite. The teacher refused to give him different work unless he finished EVERYTHING the class was doing first (DS wasn't motivated to do it just to get MORE to do so of course didn't do any of the work). His behaviour for her was horrendous (she was the one that pushed us to get testing because she was convinced he was ADHD). She was also the one that taught French, reading, writing and social studies and those are a battle because of the writing.
We're only a week into the new school year and I'm doing my best to keep out of it and give the new teacher a chance to get to know him before talking to her. The school has a meet the teacher night later this week so I'll have a quick chat and try to keep it to "have you read the IEP, please contact me with any questions and problems sooner rather than later" kind of thing.
So in other words I don't have a good answer for "how do you explain the significance of a 4 SD spread to those who don't have any understanding of testing (i.e. elementary teachers)?" It hasn't worked very well for us so far since they only seem to want to address the bottom end of things. I'm Canadian so I don't have access to DYS (maybe he wouldn't qualify anyways...) but I must say I'm jealous of those resources. Good luck and hope you're able to move towards something that works.
