I just found this thread after doing a search for the topic.
I bought a Wilson Combat spring kit for one of my 686s. It came with a hammer spring and three different trigger return springs.
Here's what I don't understand: The Wilson hammer spring made no noticeable difference at all with regard to the double action trigger pull over the stock spring. This is going by feel, I admittedly did not use a scale. If anything, I thought the Wilson spring actually felt a tiny bit stiffer than stock.
What is supposed to be the advantage of the Wilson spring?
Now, the trigger return springs did have a noticeable effect. I went with the 13lb one.