The 4" 617 handles/balances better than the 6". It is a heavy gun for a .22.
I used to have a 4" 617. It was a companion to my 5" 686. I liked shooting it fast double action but that ruined the timing. Fortunately, S&W has very good CS. They fixed the revolver two separate times under warranty but after the second time, I told my self that I was done with timing issues. I sold the 617. Also, I did not like cleaning lead build up on the throat (area where the bullet would jump from the cylinder to the barrel. It was a good revolver. I just did not know how to take care of it at the time. No regrets selling my 617.
I have not felt the want to get a .22 Revolver but if I am to get a .22 revolver I would choose a 617 with 6" with the intention of using it only for target shooting (no fast DA shots).
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For the money, I would rather have a 1911 in .45 and an Advantage Arms .22 conversion.