Personally, I LOVE this idea! My 11 year old (as of a couple days ago - 5th grader by age), is also doing great with AoPS this year, love his extras (circus, theater, spanish, etc), reads ravenously. But everything else is just ho hum. I've resisted taking him to high school level science because he doesn't LOVE it and I know he'd resent the work load right now. Even though he is more than ready for it. We don't do AoPS online either because I think the work load would kill him. Besides I *LOVE* doing AoPS with him. I feel like we're half way to unschooling right now. He's spending tons of time programming computer games, including designing his own graphics and writing his own music.
At least with my own gifted kids, I don't feel like straight acceleration in a classroom with a high output expectation is the best option. Grateful we can homeschool for the moment! Enjoy your year!