So I have been doing a lot of searching lately on how to reduce the felt recoil on my M&P 10 as well, not so much for me, but my wife likes to shoot, and it is a little heavy for her. She is pretty small. Anyways, it's hard to find anything concrete from anyone other than people saying it feels less. I wanted something a little less objective.
So, I talked with Clint at heavybuffers.com and asked what he recommended. He said to get the XH carbine buffer(8.5 ounces) with an Armalite .308 spring. He sells both on his site. At first I wasn't sure because that is quite an increase since the standard buffer is only about 3 ounces. Anyways, I bought both and put them in the gun. My first impression was yes it made quite a difference, but I wanted something more than just what I thought I felt.
All I did was, I took a weight scale, not digital, and just put the butt of the gun on it and shot 5 times with the standard buffer and spring and 5 with the new ones.(Same ammo on both) I took video of it so I could see how high the scale went. With the old set, the scale averaged 205 lbs, with the new set it averaged 162 lbs, which would be a little over 20% reduction in felt recoil.
Now I know that test isn't 100% fool proof, but I figured it is a little better then me just saying "yep it reduced the recoil".
Hope that helps!