I just bought the GP 100 after looking quite some time for a used S&W 686 pre-lock. Love it, glad I took the plunge, and will never buy another S&W as long as they are making them with the Hillary holes.
About the only difference I've noticed between the GP-100 and the 686 (besides the major extra cost of the S&W) is that the 686 has a lighter trigger out of the box. A $40 trigger job takes care of that easily. But I just like the way the 4" GP-100 feels in my hand and , like I said, its my favorite revolver.