I would not recommend skipping too many grades. It's easy for a kid to feel alienated when he's 2-3 years younger than everyone else. It's much better for the kid to be in gifted class where he can bound with kids who are around the same age range while being intellectual peers.

Another thing that helps is to send the kid a semester in a different country in a host family with a kid his age where he learns the language by going to classes with the kid there. It's a good challenge for the kid and helps him not to be so bored with the ease of everything.