Hi,
My ds is also 5 1/2 and is in year 1 at St Luke's. We've been very happy indeed with the school. The kids in year 1 are lovely and almost without exception they are all clever and rather shy little people, so your son would fit right in.
If you look back at the ofsted inspection report you will see that the reception class teaching got a grade 1 result and it is that class that is now year 1, so your son would be joining a very well taught group.
The things that mark St Luke's out as being a bit special are that it is rather a gentle school where kids are looked after very much as individuals. There are only 30 kids per year so every staff member knows every child well.
The playground is large and very relaxing to spend time in. It is open after school for the kids to stay and play and a lot of parents stay with their children which really helps with making friends. There is also a good after-school club which is run by school staff and is only open to the kids in the school. I have looked in the window often and the children seem very settled and happy.
My son went to the Mayfield pre-school which also had very nice children in it, so I think that Mayfield would also be a nice option. It has 60 children per year and has its own swimming pool, so you might like to consider whether swimming lessons would be a pro or a con in your own child's eyes.
Other than that I'd only echo what other parents have said, which is that it's really best to visit. You will know very quickly from the atmosphere, whether the school is right for your child. It can also be a good idea to just show up at 3.15pm and talk to the parents. They will be very happy to have a natter and you will see the chemistry among the parents and children which really helps.
It's probably a good idea to get names down soon as you will need to wait for a child to leave before a place becomes available. I'm not aware that anyone in ds's class is planning to leave.
I have name changed to post this btw, but please do ask any further questions if I can help.
Good luck!