I'd say 8 is (very) good. Our last was very conscientious and good with the kids, but wasn't one to get on the floor and play with them, and required a lot of reminders (like daily). We thought we were very lucky to have that. You can't have everything, so we try to balance when the au pair changes. We now really want someone who is more active with the kids, but will possibly by sacrificing organization .. We're okay with that, because we kind of look at school and child care as sharing responsibilities. If I know my kid was outside 3 hours that day, I'll sit down to read or play a game. If it was all crafts, we'll go for a walk after dinner. Even thought I think that's par for the course, I wouldn't up the 8 to a 10.
(I think if you're okay with your young kids watching tv or eating cheerios out of snack cups, and don't mind APs who think Disney is the gold standard you're more likely to be happy with the program)