Same boat here. My PG DD8 (WISC-V FSIQ 152) seems very typical on the surface. She has no OEs, she's engaging and friendly, she's not shy and doesn't exhibit any behaviors that would peg her as "different." But the second she opens her mouth, you know there's something interesting going on in her head.

She's very artistic (can draw in great accurate detail anything she sees), she absorbs information like a sponge, she can make tiny things out of LEGO that are impeccable representations of something (ex.: a 2" tall cockatiel that exactly captured the essence of a cockatiel - like the LEGO architecture series but an animal version), she out-thinks her father and me, she wakes up in the morning and immediately asks if it's possible to build a 3D printer that could create animal cells using organic material (where does she get this?). She taught herself to read at 3 yrs, 4 months and hasn't gone more than a few waking hours since without reading something. *deep breath*

But on the other side of things - after five years of swimming lessons every summer, she can pretty much just keep herself from drowning. She's been through ballet, gymnastics and martial arts with no appreciable ability in any of them. That's fine, I just want her to get exercise, not to necessarily excel but it's clear she has absolutely zero athletic potential. She is very kind to kids in her class but once she starts talking to them, you can just see the light go off for them because she isn't interested in the things they're interested in and they have no idea what she is talking about. At last year's Valentine's Day party, the teacher had the kids write something nice about each classmate on their valentine. All but one of the ones given to my daughter said something about her being smart - the other didn't say anything at all. She skipped 3rd grade and will be starting 4th grade tomorrow. I hope she finds some kids she can relate to.

I haven't read Nurture Shock (will check that out). I just wanted to say that I thought PG kids were all the types who go to college at 12 or 13 (who knows, DD might), are prodigies in music or who can do trig while still in diapers. Some are for sure, but not mine. DD is my only kid too. I had no idea just how gifted she was until I started subbing in her school and other elementary schools and realized that she's light years ahead of every other kid I've met so far. That helped me see that our normal at home was anything but normal!

Your son certainly sounds PG to me. Have you tried JHU CTY classes for him? His school might allow him to use them in class to further challenge him. My DD will be taking a critical reading class from them during her school day instead of being in a reading group this year as she's far outpaced the level of books they cover in 4th grade.

Sorry if this is scattered. Coffee hasn't kicked in yet.