Been there, done that, currently doing it, sort of.
Disclaimer: I am not in the US, so navigating a rather different school system, but it has been my experience that the needs of gifted kids and the inability of educators to recognize and meet them are pretty much the same the (Western) world over. YMMV.
DS10, probably PG, currently a fifth grader, has been what one might call mildly accelerated. He was born just after the cutoff and was entered early into elementary school after a tolerable, but not terrific time in the local preschool. His preschool teachers were kind and accepting and he was never a total outcast, but no one really "got" him either, and he did not really have friends.
We decided against the local public elementary and enrolled him in a catholic school which stressed both community and rigour and happens to draw from a high SES demographic and it has sort of worked alright without further acceleration. He was the youngest in his grade though not by much, since there did not happen to be redshirted kids in his class. Socially, it worked alright, not really popular, but not an outcast and he did have friends, though I did a lot of behind the scenes work arranging play dates! It was never smooth sailing. Academically, by third grade the mismatch became rather glaring, he had meltdowns in the mornings because of the slow pace and the amount of repetition and a further grade skip was mooted (and discussed on this forum) but we decided against it.
The most important con in our case was that HE decided he didn't want to - he had worked hard making friends and didn't want to lose them before he had to, ie before having to transition to middle school where kids from his elementary tend to disperse all over town again,
For us the main reason against it was that he would have been an 8 yo in middle school (starting in fifth grade) and the one school with a gifted program is on the other side of town and huge. He simply wouldn't have been ready to cope with the EF requirements, he is having a hard time now as it is (we have been told he easily qualifies for an ADHD diagnosis if we wanted or needed it, but it hasn't been necessary or helpful so far). Also, he never liked being the youngest and enjoys that in the gifted classroom, with so many accelerated kids, he is smack bang in the middle if the age group. I feel that the maturity gained in four years of elementary helps him navigate the social minefield of middle school now. He enjoys doing grade based academic competitions and is proud of no how well he is doing.
However.
He did have to suck it up in fourth grade - even though the standards in that elementary are truly and certifiably high and he did improve in writing and LA and the benefit is noticeable in comparison to his classmates now (a number of which have skipped fourth in order to directly enter into the gifted program) and he did enjoy a lot of last year lets do fun stuff before you all leave, he was still bored out of his mind most of the time. And he did mention how glad he was to be finally done with elementary school and how much better he likes it now in the gifted classroom. I did not realize quite how unhappy he was - well I did, he actually had to go to therapy for suicidal ideation, but I did not think it had to do so much with the school - still do not know now, to be honest, but I think it is easy to overlook just how much harm not acceleration can potentially do, even if it looks like the least worst option at the time.
I'd also like to point out that while it is true that one ought to plan for a year at a time and try not to stress about potential problems down the road, I believe it is crucial to research what options there are AFTER elementary school for your giftie and how the skip can affect those options. In our case, I feel that not accelerating further has set DS10 up to be successful in gifted track middle school, but it appears to have been a narrower escape than I thought.
