Only read your op, not the whole thread.
My situation is slightly different to yours but Ds and dss are in the same year group and didn't get on very well and are very different at school.
They were at same (large) infant and junior school until year 4.
When we moved we decided to try them at different schools as smaller schools.
It worked really well - gave them both a chance to have their own identities and not be compared to each other. Both were walking distance so no problem getting then there, I had to walk past one to get to the other and by that age they weren't collected from the classroom door anymore.
We didn't hesitate in sending them to different senior schools, and as they are so different the same school wouldn't suit them both anyway (having 4dc's, 2 with sn, I realise now that not every school will suit every child).
It really has worked out brilliantly and I would definitely do the same if in the same position again. Both get the support that is right for them and have their own sets of friends so no issues there either.
They even get on with each other better at home now too 