Me too Crisc. You may remember our story last year was very similar. I think you have a good plan. In our case the problem wasn't caused by boredom, or the teacher totally not getting C and doubting her high intelligence-overtly!-, or the fact that she wasn't provided with appropriate learning materials....It was a combination of all three. And who she is just made a bad situation that much worse.
Play therapy with a psyd. who understood that she is truly brilliant and TREATED HER THAT WAY....was a life saver for us.

However, I have to say(and I am a person with very few regrets) I totally regret not pulling her out. It was hands down one of the worst decisions I ever made in my life. I had no way of TRULY knowing what was causing the disress and I did the best I could with what I had......
But because of how she changed when school ended and how great things are this year, It's clear I should have trusted my intuition, but oh, how I struggled with it!

JB dad and especially you Crisc, sound like you have similar situations......but only you are privy to all the facts and who your child is.

Good luck and trust your gut

((hugs))