General accepted rule of clubfitting is too stiff= low and right, or just lower in general and shorter distances, correct??

Yesterday I demoed a set of irons w/ PX 6.5, which I assumed would be too stiff for me. Here is where it gets confusing: distances were shorter than normal, as I figured with shafts that are too stiff, but distances were shorter due to a ballooning ballflight?!?!?! What gives?? And the best part of the whole situation was the fact that I haven't made such good contact with irons all year (sweetspot every time)!