I think it's easier to skip the early elementary years. Also the early elem. years are the most mind-numbing for GT kids. Our DS skipped first grade and is still friends with a couple of the kids he "left behind" -- that doesn't have to be an issue. You can make play dates, do rec sports, etc., outside of school.
Our son was also an excellent candidate on the IAS. One grade skip was not enough, and we transferred and commute to an accelerated program for HG kids, which has been a good fit.
There is usually a way to undo a skip later on, but in my opinion, high school would be the time to do that, when there are more opportunities for appropriate classes and dual enrollment.
We do not regret the skip for our kiddo. If your son is really into competition (academic or sports), that is something to consider. It was not an issue for our son in early elem.
