I don't recommend going under 17lb main spring, especially if you're using whatever primers you find. It will have minimal impact on your recoil impulse compared to stuff like tuning the firing pin stop profile.
Oversprung pretty much just refers to the downward dip from going into battery, it comes from a heavier recoil spring relative to the ammo you're putting through it. Lower power factor generally means you want to use a lower rating recoil spring. 9 is a great starting point, but you can try 7, 8, 9.5, variable, etc to get the impulse you actually want.
I'm a firm believer in "if it works for you, it works for you" so you don't have to change anything if you don't have complaints.