Tried out the Wolff guide rod and 19# spring (XDService 40) and was impressed. No offense to Don (I have his setup too). After 100 rounds, zero malfunctions of any kind and recoil was very manageable. I think the 19#is just enough extra power (the Wolff 17# is equvialent to the factory raiting) for me. I bought a 21# spring to test it but I don't think I will bother to use it at least for now. Until I have reason to switch guide rods, I think I will keep the Wolff in.