I personally think a factory DA pull should be around 10#s. However, there are many S&Ws out there heavier than my 12# max Lyman can read, some approaching 15+#. I don't care for heavy pulls like that.

My 629-2E was pushing 15#s. I installed the middle weight rebound spring out of a three pack, 12# IIRC, then backed off the strain screw until it reliably rebounded. After testing primer reliability, permanently modify the strain screw. When all said and done, I had a DA pull of around 9.5# and a SA pull of 2.5#. This was with polishing internals too.

However, I firmly believe the reason for the overly strong springs is intentional due to safety. Since S&W's hammer cocking notches are only about .006", the notch itself and the trigger sear need to be about perfect to prevent push-off. The slightest buggering of either surface can induce this, but overly heavy springs can counter or hide push-off.

When lightening my 629, I ended up with push-off due to a slightly buggered trigger sear. I had to re-cut the sear then everything was kosher again. So lightening springs can open other worms, but if it was built properly and remains that way, you should have nothing to worry about.

Just an aside, I "prefer" my DA pulls around 7#, but not every gun is capable. Other than that, 8 or 9#s is about the sweet spot for me, the lower the better. Everyone is different, but the smoothness of the action is usually more important for most than what the exact weight numbers are. So what you prefer is personal and will need determined. This will also vary depending on purpose. A gun that I use for targeting or hunting will be shot in SA, so DA isn't that important to address.