WildPete,
I have tried all the way down to 12lbs and worked my way back to the 15lbs spring on a W74 guide rod. I believe every gun is going to behave a little different so the range between 14-18lbs is going to be a sweet spot. My 114-133PF ammo runs with the 15lbs spring in my S. I bought the 12-18lbs springs from Wolff. Cheap $ for spring tests!
I like the recoil spring test Atlas does for tuning a 2011. My recipe is best splits grouping (6 rounds - 3 splits at 21') wins the spring test with the preferred ammo for the barrel. I ran weak 115g tuned for my PCC thru Syntech 150g. My barrel preferred a 124/125g round nose. The S ran smoother with plated/FMJ (124) versus coated bullets (125). I started with the 14 spring, worked up 1lbs to the 18, and came back to shoot the 15 again. IMHO, it is worth the time performing this test for your gun. 124/125g power factor was 130-131. For me, the best 124g was Freedom Munitions New and 125g coated was NC Shooters Blue bullet.
I run factory ammo, not personal reloads. I'm sure the reloaders will have more fun!!