You must check the model of Gpus, memory isn't important (as achow101 has explaned you) and it limits mining in a few cases(ethereum) and if you buy unknown gpu model/manufactor probably you won't configure it to work correctly.
Sorry for the late response, I've totally forgot about this post. Ok, let's say that I find a few gpus that have the average to lower than average cores and clocking speed. Would that payoff in some case? Would it be worth doing that at all even if I can find a 10+ average GPUs that are considered good for some alt-coin mining?