I had a grade skip when I went to school, and my wife had two grade skips. Neither of us thought there was a benefit.

So for our kids, we didn't attempt a skip, despite them being some of the older kids in their class. Socially it has worked out very well, as they are both well adjusted and popular.

Academically, it helps that our local school system is one of the best in Massachusetts, so my MG/HG DD13 still has academic peers. My DS10's skills are higher, so he doesn't have academic peers. Realistically, a two year skip would be meaningless for him, and anything beyond that I think would just be unreasonable.