I normally advise just one pair too, but recently have seen a few rule exceptions, Mobert is one, and there is a guy from Brazil on here w/ a large # of saddlebacks.
A friend has a 60g cube loaded w/ saddlebacks and percs, not sure how many, but as soon as I saw it I expected probs, but they do seem to be doing OK.
I notice pecking/keeping in check almost always, and wonder if any die that don't get noticed, but I don't see torn fins and such as I would expect.
A local breeder here says if more than 3, there seems to be less probs, one dom fem, a male, and many sub/non sexed males from my understanding.