That's a good overview of the strut/seat/mainspring situation.
If one has an older Sig, I'll say that upgrading to a newer mainspring assembly makes a big difference in the DA pull. I yanked the old-school steel seat/strut out of my P6 and put in brand-new parts with the plastic seat, etc. (I forget if I used the "New-Style" combo or the "E2" combo--they both work). Night and day. Gave the old P6 (which is known for having a shit DA trigger) a reeeally nice DA pull. I think I used a 19lb hammer spring from Wolff, as well.