You sound a little calmer and more focussed TripleB. It's never easy to make these decisions but it often goes better than you imagine, especially as you are taking a considered approach.
Our DD is not sporty so that was never an issue. Her maturity and executive functioning developed, or were more exposed by each acceleration. We can see her confidence has expanded with the prospect of advancing again this year. It flows into her social skills too.
We offered her a trial of one term, about ten weeks, for this skip. As it turns out, it is unlikely to be needed. A trial needs to be at least 6 weeks to give everyone a fair run. I think the idea of it being a trial just allows all participants to feel more comfortable, especially parents. If you go that path then do it as soon as possible so it doesn't get caught up with concern over the end of year exam.
About the math versus reading....we thought DD was verbally advanced not a math kid until grade 5. Turns out she just didn't have an opportunity to demonstrate math reasoning until then and took off. She hated times tables and rote learning. Lots of kids show different aspects of themselves at different times
