Interesting thread..... Unfortunately, most of the knowledge regarding these fish is anecdotal rather than scientific.
According to the preeminent researchers on the subject (Stauffer and McKaye) these are the sizes of a representative sampling in their study "The Midas Cichlid Complex in Two Nicaraguan Crater Lakes:"
(standard lengths listed; add another 10-12 cm for tail lengths)
A. amarillo 107.6-154.5 cm
A. xiloaensis 124.4-170-5 cm
A. sagittae 121.2-163.1 cm
A. zaliosus 110-124 cm
A. labiatus 129.4-140.6
A. citrinellus 130.2-139.5
Of course, there they didn't go cherry pick the fish in any way, but they do feel their sample to be representative of the species. Note how much smaller these fish are (again, on average) than what we see in aquariums. I've had all but one of those species exceed a foot in length in the aquarium (and the other one is well on its way). Still, you just won't see a bunch of fat, 14" Midas cichlids, with softball sized humps swimming around Nicaraguan lakes too often!
The point isn't how big or small the fish are. Most of us know they all get much larger than indicated...... The point is the high degree of similarity in size.