Our one and only sprog went to a very small local junior school for around 2 years - initially very good and then we had a bleeding heart (in her mind not her body) headmistress arrive and wow what a change for the worst! Suddenly we were told we had to STOP

helping her with her reading and writing outside of school hours (she wanted to I assure you as I'm not one of those flash card from baby in the womb ambitious type of mums I can assure you) AND

because she was a tad bright (must take after Barman eh

) she wouldn't be allowed to have additional work given at school to strech her BUT he expected to WAIT for everyone else to catch up.........................!!!!!
Not a tough decision for us to look to change schools then and like you we investigated the fee paying options - found a nice one (based on what the kids appeared to be like on our viewing mostly - happy, polite etc etc) in Windsor and prepared ourselves for the next few years of being partially brasick

She stayed there until 11 and then took her common entrance exam because we'd been doing our research meantime and found to be a marvellous non fee paying Catholic school (sorry the religion bit always creeps in somewhere doesn't it) and once we'd convinced the mafia (sorry Nun's) that despite not being 'C' ourselves we didnt sacrifice chickens or burn black candles EVERY night she was accepted.
Stayed there until 18 and left us for Univille.............
You really do need to do your research and shop around and then go with your gut feel on what's best for your childand you - Not saying that ALL fee paying schools are good (I do know some bad ones) nor that all state schools are bad either - but times have changed no doubt about that and education service are not what they were.
Mind you after all that have to say I failed my 11+ in the old system and then ended up going to a crap(ish) state school myself - oh those were the salad days weren't ??????