I'm doing the AQA certificates in chem and bio . . . The specimen papers are much harder than the ordinary gcse ones but not too challenging. I don't think many state schools are doing it and generally private schools do better than state schools, so I hope the boundaries aren't too high. And also they can't give like only the top 10% A* cos there will be many candidates who would get A* at gcse, so I imagine around 30% will get A*. Also, it works in our favour cos as u said we're the first year ever so the grade boundaries should be lower.
Good luck!
Btw I go to a good private school in the northeast of England (contrary to popular belief, there are clever people in Newcastle!)