Besides the shape of the barrel what's the difference between the SSR and a regular 686 as sold today ?

finish, for one. bead blasted on the ssr.

my ssr came with wood and hogue grips.

mildly chamfered cylinder that is adapted to take moon clips.

the best difference, in my opinion, is the ability to change the front sight without the use of tools (spring detent vs pin).

newer models do NOT have a trigger stop.

i own both a vanilla 686 and the ssr, but at different lengths. the full underlug and 2 inch longer barrel on the plain 686 seems to help me shoot it better most days.

either way, you will wind up with a modern s&w revolver