Just to make yet another echo in the room, I'd also recommend starting now. The cogs of a public school turn ever so slowly, so even if you start now, you may not see the end result for several months or even another year.
And, as you've already heard from some pretty wise folks already, I'll only add that as much as you're hoping your kiddo will find a place of acceptance and normalcy, it might not happen at that IQ. I had to readjust my goals to helping my child accept their own gifts, toughen their skin, and find activities outside of academics that offered more chances of "normal interaction".
