The Walker trigger was good, or could be tweaked to be very good. The new X Mark Pro trigger isn't bad, it's pretty average for a modern day trigger, but it isn't comparable to a high end trigger, hence the upgrade.
I had a 2009 mfg 700 SPS youth in .243 that had a X Mark Pro trigger. It would fire when the safety was switched from safe to fire. The trigger was not altered from factory state and the rifle was pristine (it wasn't a maintenence or neglect issue). Lots of people called me a liar, but I am not one and I hope my reputation on this board is above that.
It was sent for warranty repair (this was before the recall) and the trigger was replaced.