To throw another anecdote into the fray, my other dd has not fluctuated in her relative position with peers unless it is to pull further away. There are HG - HG+ kids who test HG early on and continue to test that way throughout their school careers. Your dd could certainly be one of those too.

That's why I always say that the best advice we were given when skipping dd a grade was the look at what met her needs right now and not try to have a crystal ball about what her needs might be in the future. We haven't regretted moving her ahead. It was the right choice.

Study Strategies for Accelerated Learners