I assume by saying "I have a 617 thats 4 inch", you mean a S&W 617(22lr), not a Taurus 617(357mag), correct? The 6" 992 will be a bit front heavy, but (in theory) should be more accurate at longer distances, given the longer sight radius and barrel. And, since you already have the S&W with a 4" barrel, I would think a 992 in 4" would be a bit redundant.
However, the thing with the 992 is that it is designed to accommodate both 22lr and 22mag ammunition. The 22mag is ever so slightly larger in diameter (and someone please correct me if I am wrong, here, as I am always willing to learn), so the barrel bore will be optimized for that round, and the 22lr will be ever so slightly "loose" (for lack of a better term) in the barrel. That said, I'm not sure how much more accurate the 6" 992 will be (using 22lr ammo), when compared to the 4" 617, which is optimized for the 22lr cartridge.
Now, the 992 is a fine gun from what I have read here, but if getting the best possible accuracy over longer distances using 22lr ammo is your primary objective, you might want to look for a 22lr dedicated revolver. Just my opinion, though.