I installed the M*Carbo spring in my X-bolt. I don't have a scale to measure trigger pull, but if I'm honest with myself, I only noticed a small change, even at the lightest setting. I have several other rifles that break a lot more cleanly and with a lighter pull. I'm planning to go to a Timney. That said, given then number of positive reports above, the Carbo spring is a cheap interim solution to try out.
I will say that the online video on how to replace the trigger spring was fantastic, and one of the sharper DIY tutorials I've seen over the years.