I had this dilemma when DS was in reception but made the decision to move him to a specialist S&L provision in the end. In DS case, he had a very severe speech and language disorder/ delay with an additional diagnosis of verbal and oral dyspraxia !
Everyone loved my DS at his Ms school, the children and staff were very lovely and DS was very happy. However, I was selfish, I wanted DS to communicate, I wanted him to make actual friends instead of friends who saw him as a baby ( they children were very nice but he was babied a lot), I wanted him to gain verbal speech and communicate effectively so that he can navigate the world etc. Speech and language provision at his MS was very insufficient. At his specialist S&L school he gets speech and language therapy every day delivered by an SLT.
I could of waited to see how he did at his MS. But I didn't want to take the risk. It also helped that I used to work with teenagers who had very severe speech and communication difficulties and displayed very severe behavioural problems. Some of the staff members confided in me that when some of the teenagers were younger, no one taught them any forms of communication or worked on their speech and language difficulties ( whether in their specialist or mainstream school) and as a result have very severe behavioural problems due to the lack of communication skills. This swayed my decision even more.
DS went from saying 5 words to around 200 when I moved him. We have come conversations and arguments
. Which I thought would never happen. He is however still severely delayed compared to his age. Also, if we hadn't gone to the socialist school I wouldn't of known about high tec technology, which has helped DS tremendously since his got it.
However, I think DS has suffered socially since attending his SS ( I don't know it this could be because he goes to an out of borough school) But the majority of children come from all over the borough, so it's difficult to arrange play dates. The children have different needs which can be quite difficult to accommodate. DS loves going to noisy places ( cinemas, fun fairs etc). Some of the children can't tolerate loud noises so for their sake I have to accommodate to their needs if I plan to take them and DS out.
It also goes in your favour that your DS is academically keeping up with the curriculum. There are some children with severe SLCN that are exceptional in their academics. DS wasn't like this, even though he was above average cognitively, due to his SLCN he wasn't able to access the MS curriculum. Also in reception they seem ok, it's when they got older within the primary school years, social demands and expectations increase that may have an impact. Though you may never know.
I don't know if I did the best thing for DS, I guess you have to look at your current situation and see from there.