I struggled with the same choice a few years ago. After settling on the 6" barrel, I went into my LGS and held the 4" 686 just for comparison. About 45 minutes later, I walked out a with a new 4" 686. However, I knew that one day I'd have them both, and that day came just a few weeks ago when I found a pristine, used model 586 with 6" barrel and bought it at the same LGS. IMO, that's' the most reasonable outcome you can hope for.

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Northwest Ohio