I have had both -Stock 2, and Shadow (actually, I sold my 1st shadow) , but still have one in my basement, in NIB-unfired, I purchased for a friend as his paperwork lapsed.
unless you bench these guns, in a rest, you will be hard pressed to tell the difference,....although I find for me, the S2 was just slightly more accurate. Maybe having a bull barrel makes that much difference. The SA trigger of these guns are great. OUt of the box, it is my opinion, that the Shadow trigger in SA is better, but with my S2 worked in, it is on par with the shadow. The DA trigger pull with the Shadow with a lower weight hammer spring is "different" than the S2,....the S2 has less travel in DA, but is smooth now that it is worked in. Both guns seem to want to get back on target quickly, all on there own,.....if you relax and press the trigger with a decent sight picture, the guns do all the work for you. I think the accuracy will change based on which configuration of ammunition you use. Very easy to get good hits with either gun, even on steel plates out at 25yards+! (see signature below*, link to hitting steel with S2)
I like how stiff the safety is on the Shadow as opposed to the S2, I hit my S2 safety a few times, as I placed finger up off the trigger to do a mag change.