You can definately overdo a light DA pull. Remember that the weapon still has to do a lot of mechanical things to get ready for the next shot and reducing the spring tension too much reduces reliabililty and the speed with which you can get off the next shot. Smoothness and consistancy of the action is more important than the exact weight.

BTW, 2-4 lb triggers are a whole lot easier to do on a keyboard than in the shop.

The only minimum revolver pull weights I've ever seen in the rule books (been a few years) were for single action. Which is why most PPC revolvers are/were DA only, there was no way they could meet the SA requirement.