"Keep in mind, that with a 3-4" barrel, you won't be able to shoot tight groups. You might be able to hit a man-sized target at 40-50 yards, but they are generally suited to close range"
Definitely not true, over here in Europe we shoot 25m (ca. 27 yards). I am a total newbie, have never shot handguns before. Guess what: With the 4" barrel I shoot groups with ca. 6 inch height and 14 inch width in quick shooting da, with my M14 6" I shoot single action groups of 2 to 3 inch height and 6 inch width.
The S&Ws are some of the most accurate revolvers and handguns ever built. So accuracy depends on the shooter, not so on the gun.
If you go back from 6" to 4" the sighting line goes down from 8" to 6" and your groups will be 1/3 bigger, that's all.
I think 3" in the minimum one should choose, especially with the K-frame as it isn't *that* small. 2" barrels is something for J-frame BUGs, those guns doesn't even have flat mainsprings so they're a compromise already.
3" is perhaps the best .38 special barrel length, 4" for .357 and 5" for .44 magnum, I like 6" for target shooting of course..