My Sig Target 1911 was 4.5lbs out of the box. After some buffing and tweaking, it's now at 3.5lbs. I have a 80 to 70 shim sitting on my bench. I keep meaning to try it to see how much improvement it'll make.
I should clarify....changing the parts to Series 70 ones AND doing a trigger job / polishing will make quite a difference. Changing to Series 70 parts just happens to make it more convenient to work on.