We did a multi-grade skip and it has worked well, but it is not the best solution due to the pace of the classes DD10 is in is still the same old slow as molasses pace (according to her).

My advice would be as follows:

If the results come back and it looks like a skip would be recommended express that you are very excited about this option and that perhaps the school could allow it to happen on a trial basis, (the length of which could be the first marking period, or half of that depending on how long a marking period is at the school) let them know that you understand that while it may look on paper like the skip will be a good fit, you would appreciate them giving your child an option to change out of the multi-grade skip if it proves to be too much.
My reasoning here is that the school that approved DD's multi-grade skip was convinced that it wasn't going to work and that they wanted to be sure that they gave DD enough time to show that it was a bad idea. In reality, I was fine with giving progress report time (5 weeks) as a trial period, because I knew it was going to fit due to Mommy intuition, and saw that if I got upset about their insistence of calling the time a trial they would refuse all together, so maybe if you bring up the idea as being "for a trial period of x weeks" they would be more willing to let it happen. It gives them, and quite frankly you, a way out if it turns out not to work for whatever reason.
If you are successful getting the skip, I would put together a summary of your son's traits and behavior's along with a list of websites, like Hoagies, and the educator's guild Davidson and a short summary of "typical" gifted kid traits your son has and then make an appointment to see all of his teachers and share it with them. While I had 1 teacher get mad at me for doing this (she thought I was insinuating that she didn't know anything - which she doesn't- about gifted rather than seeing it as a way to better understand DD), all of her other teachers were thrilled to have basically a list of what to expect from 9 year old in 7th/8th grade.
I put things like:
1)Please do not think that she will already know everything you are going to be teaching - she will be in your class to learn something she doesn't know yet. It is typically the pace at which she learns that becomes an issue, not that she knows the entire subject already.
2) When she is "in her learning zone" she hums - if it is distracting to others please remind her to hum inside her head
3) She will make seemingly unrelated links between what you are teaching and other topics - before telling her that her link is incorrect let her explain it - it maybe wrong, but most of the time it is correct. Her links are usually not the ones you would think of, but are usually correct.
4) Although intellectually she is at least a middle schooler, she is also still just 9, so please understand that her penmanship and other executive functioning skills will not be at the level of other in class.
5)DD also happens to have an incredible amount of empathy for others, and may react more strongly to things than you would expect, it is not because of her age, but rather her "excitability". If you notice that she is quiet or looks upset, please let me know so that I can talk with her and find out what it is that bothered her - often times she will not know right away and needs time to process what the trigger was.

etc.

There were a few times when the empathy and humming were noticed by teachers and I was informed about both - the empathy so I could help figure out what was up and the humming because something was at the appropriate level.

Sorry this was so long, hope it is helpful.
Good Luck