I guess the pedantic answer is 8,8,8, does not matter. Optimal defense with Q9xx/Qxx is to play so that when the fourth case occurs, either holding is equally likely from declarer's POV. They can duck any percentage of the time with Q9xx (including never), so long as they duck C times as often with Qxx (where C is prob(Q9xx)/prob(Qxx)). If they don't do that, they can be exploited.