You learn pretty quickly that reducing spring weight is not all there is to it. A 19lb. hammer spring along with a quality reduced power sear spring is certainly low enough. I got my recently purchased Springfield Armory Garrison down to just under 3.5 lbs. with nice feel. Not sure what it was from the factory but i know it is much improved now. I finally got a sear jig, a simple and reasonably priced one from Ed Brown. I used the stones from a Lansky knife sharpener and they did fine following the detailed instructions on Ed Brown's website. I could do better if I had all the specialized stones for smoothing out the trigger and sear ways in the frame. There are many surfaces that have movement on a 1911 action.
This Garrison has proven to be an accurate gun, certainly on par with some of my revolvers with similar barrel lengths. Improving the trigger and sights has been very worthwhile.