My late in the academic year DS started Reception in his correct year and was fine, he's physically very small too but apart from being a little more tired than his November born big brother there was very little difference. Funnily enough his best friend was very tall and an early September babe so they did look a little odd together
He did very well in his 11+ getting into a SS grammar even though he took the exam about 10 weeks after his 11th birthday.
As an EY practitioner, albeit a Nursery School one, I can say that we are well practised at looking out for "late born babes".
I would think hard about taking him out of his chronological year group and certainly wouldn't want to take the 11+ in year 5 and miss year 6 which is a year full of coming of age milestones.