What gives the most certainty of a good state education?
It's living on top of a great Comp which does well by all abilities, and living next to that kind of school at the time if application.
I think you can accept that such a school whilst having some disruption will be on it and manage it and your child (who presumably isn't a totally delicate little flower) will be able to cope, learn well and do well,
With Grammars you have no certainty of entry and in a full Grammar area, the risk of the sec modern which may well be less good than a Comp.
There's no absolute certainty. You have to look for the thing which gives you most peace of mind both now and in the years leading up to Secondary and during it. If you live on top of a good Comp which has been historically good, then that is the best you can do.
If you go to a Grammar county you face months or years of not knowing which school your child will get and probably prepping - because Vik will be the kind of parent who will feel the need to do lots of prep if going for a Grammar, especially if she's moved specifically for them.
Of course if you are willing and able to pay as a back-up and can get into an independent you feel is acceptable, then you have a back-up if you don't make the Grammar. You have to decide if you really are willing and able to pay because if you are, it does totally change the situation, because you have a back -up to avoid a school you don't want, which other people who can't or won't pay don't have.
So actually OP, I would think about the independent issue more first. How willing and able are you to pay if it comes to it? This needs to be a driver in your decision making. If you are willing to pay, you can also choose more widely where to live and perhaps save money on house purchase. Again, not socially fair, but a reality for many people and a way that some get the education they want and avoid the Grammar issue.