It pains me to say this, because Origami, my wife and Vogel have all said the same thing, and I disregarded it, but I believe a Gen 3 has enough better a trigger (specifically less creepy travel between take up and trigger break than the Gen 4) that the Gen 3 is a better pistol for doing your personal best work, and it is less tiring to shoot over a high round count (because the trigger has less creep to work through).
I think the Gen 4 is fine for personal defense, and I really dig the accuracy, slightly smaller size and texture. However I plain shoot a Gen 3 better.