Wirral Grammar is a great School, my DD goes there.
Would I uproot for this School probably not, knowing what it is like. I don't think it's worth the moving.
But hey , I don't know what the Schools are like in North Wales.
You also don't need to live on top of Wirral Grammar. (probably within 7 Miles)
My DS goes to Brackenwood School (across the road from WGSG) , I think this is a nice pleasant school and would have no problems recommending.http://www.brackenwoodjuniors.co.uk/
I have heard Higher Bebington is a very good school and pushes the children to 11+ but maybe difficult to get in. Kids in my sons Class have left to go to Higher Beb which tells you it's in demand.
It has a Outstanding Ofsted report,http://www.higherbebington.wirral.sch.uk/home.shtml