mmm - I am never very good at working this out, but if she is 4 oct 2009, won't she go to school the year after?
Is she 2 now?
You have plenty of time - have you actually looked at the other state primaries? What are your reasons ofr not liking them?
Anyway, if you can afford it, applying to state and private simultaneously seems a very common strategy for many parents.
And of course the answer to your q is 'depends on the schools, depends on the child'. I went to a private primary school and a 'direct grant' secondary (half private, half selective scholarships paid by the state). My brother and sister were both educated in state education throughout - one at a grammar, one at a dubious comp. We all have degrees, my grammar school brother has a phd, we all earn about the same money, and have similiar outlook in life. My private ed just meant my freinds lived further away.