I have a 617 with a 6" barrel and the six shot cylinder. Very accurate gun and drill and tapped for a scope base. Since you want to mount the optic, I wouldn't get anything that wasn't factory drilled and tapped.

I have used mine with a scope and red dot for squirrel hunting and have no complaints. The 617 would make the perfect companion for the 686 you already have. Same frame etc.

I had to search a bit to find the six shot version but I'm glad I did. You can still find them on the auction sites if you're willing to be patient.

John