Yes, sounds fantastic -- and just what I'd love to see develop near us!
As others have mentioned and you are obviously aware, for us it is the pace of learning that makes our DC difficult to "fit" into a grade. I would love to have a multi-age HG+ peer group for learning/socializing/creative play. There's more I would say about our experiences of grade acceleration, but it seems you are most interested in info on academic development.
FWIW, here are broad strokes for our oldest, DS7:
Age 3: k math and 1st reading, no real interest in fine motor
Age 4: 3rd grade reading, 1st math, still not much writing
Age 5: 7th grade reading, 3-4 math (although not fast with math facts until 6), 1st writing, (with precise spelling.) Not sure about science/history grade level, but was devouring jr. high nonfiction science and history books.
Age 6: 9th gr reading/comp/vocab, 5-6 math (being a perfectionist, he mastered math facts because of weekly timed tests). Finally started writing and took off on that. School placed him at 6th grade writing, but I'd say 5th, for no real reason.
Age 7: not yet halfway through...
