oldave, i think you are talking d3. i feel like you need a little less to pull down in d3 than d2, so 8 may be enough with an a+ in d3 but is probably not enough with an a+ in d2.
also, to the OP, if you are just slightly over 10, you might not have put in enough effort yet. it can take 12-14 easily with lower prestige, and i don't think it requires somebody else trying to pull them down too.