I am shooting a SFx as well. I have the W74 tungsten guide rod and am using a Wolfe Commander length 15# spring. I have 12#, 13#, 15# and 17# besides the factory spring and I change them out according to the load I am shooting.
Other mods are:
Freedomsmith Pro model trigger with Galloway Precision spring kit.
Galloway Precision grip tape
Taylor Freelance brass backstrap
Holosun 507c-gr
She is running like a champ!