Never mind- I found it!
Every state is different, so I think you really need to investigate the situation as it applies to your state. I don't feel like I can offer general advice on this one. I'm fortunate enough to live where there are not a lot of hoops to jump, so I can't say whether a homeschool grade skip might be beneficial or not.
One thing you may want to bear in mind is that a grade skip will put your son at a slight disadvantage when it comes to special awards, talent search and academic competitions. These are usually grade specific, and not just organized according to age.
My family usually tests each Spring for our own information. We do order "up" 2-4 years. It's not a perfect solution though, as I'd really love to have the option of ordering every subject's testing ala carte. DD gets math anxiety if we go too far ahead, but it is never enough on the verbal side for her.
Not sure of that was helpful after all. Sorry! Wish I had more to tell you.
