One of the reasons we chose to homeschool instead of fighting the system to try to get them to leapfrog/multiple grade-skip him through public school was so we could try to slow things down for DS7 without boring him. We are able to introduce subjects he'd NEVER get in school, like Arabic and downhill skiing, to broaden his experience and keep him interested without pushing the usual curriculum order.
I think we usually assume that what the schools teach is all that matters, but there's a lot of material out there in all subjects that isn't taught in most schools and is worth learning. Sometimes thinking laterally can provide all that a child needs both in terms of depth and difficulty, but without the rush.
My reasons for wanting to keep DS7 fairly close to his age level (more or less...):
1) He likes sports, but he's not a superstar, so I'd like him to be able to participate at his age-level. It's the best fit.
2) He does reasonably well socially with kids fairly close in age to him--within 0-3 years--and I'm with Dottie that more separation than that seems a bit scary to me.
3) He's deep but not fast, and while he needs a significantly greater complexity of material (3-6 grades beyond age level, depending upon the subject), he also needs greater time to process it. Grade acceleration doesn't seem like a great fit for those specific needs.
4) The thought of college at 12 of 14 brings on massive waves of anxiety. I don't want to do that if I can help it! Slowing him down by "going broad" helps to allay my anxiety. (It's all about me, there!)
I'd have to say, though, that if my only options were to bore my child and go slowly or to rush through elementary school, I'd rush. I don't think the options are truly *that* limited, as acs and G3 have rightly noted. There are ways to afterschool and use extracurriculars to provide some challenge, which is enough for some (not all!) kids. But if we're really locking it down to just those two choices, or if you have a child (like mine) for whom afterschooling and extracurriculars could not possibly make up for 7 hours of solid in-school boredom, then I'd say rush.
FWIW...