I would think that if the tolerances are good, if the chambers are good, if the barrel is good, and the bullet is being spun fast enough to stabilize, then a 4" barrel would be fine. If you prefer the balance with a 6" barrel, then perhaps an old K-38 would do the trick. (But good examples are getting harder to find.)
I've found that, provided the ammo is good, accuracy is a characteristic related to the individual gun, rather than barrel length. Well, there's the extremes, though. My 442 and my DW M12 with 2.5" are less accurate than my revolvers with 4" (or longer) barrels.
I'm not trying to steer you in this particular direction, I'm just giving you another option. I have a beat old 686, and I love it to pieces. (Literally, if I don't send it in for a tune-up.)