You can get the 686+ in 5" also. It is currently made in 2.5" 3", 4", 5", 6", and 7".
It's already been stated in this thread, but the 6" does give a meaningful ballistic advantage and a longer sight radius.
It should be understood that the .357 cartridge is not limited to a single level of "power" but can be loaded from levels less than .380 all the way up to double the energy of .45 ACP. Because of this, some people call it "versatile" but its critics point out that there isn't that much versatility in its practical use. However you see it, it can be loaded with a wide variety of power levels. Because the barrel length has a very substantial effect on the velocity, the longer barrels give an even greater variety of possible power levels and perhaps more importantly, they allow one to achieve "enough" velocity with less powder. This, combined with the greater mass, results in significantly less recoil. For example, let's say you want a 158 grain bullet at 1100 fps. That is a useful load whether for self defense or deer hunting or just practicing for either purpose and its quite good for plinking steel or whatever. With the 6" barrel, you could load it possibly 300 fps faster, but it may just add recoil and no improved effect so it might be more sensible not to. So to get the 1100 fps, with a 3" gun, you might need 17 grains of a "Magnum" (slow) powder. You get loads of blast, flash, and gas. With the 6" barrel, you might only need 6 grains of a faster powder to get 1100 fps. It burns more completely and results in less flash. Your powder consumption in practice is less than half as much. There's meaningfully less recoil.
In my experience with a 3" barrel 686+, it does not have much more felt recoil than 6" if I'm shooting the same cartridge. The 3" develops so much less velocity that the recoil impulse is lower and even though the gun is lighter, the recoil velocity is not much higher. Now if I was shooting the same velocity from 3" and 6", the 3" would have a LOT more felt recoil.
Balance and handling are somewhat subjective. I feel the 3" is too fast and unsteady. With the full-undlerlug of the 686, I feel the 5" has just the right balance. The 6" might be a little front-heavy. If I were hunting, and especially with a scope, this wouldn't matter -- I'd get the 6" or 7". I think some half-lug 686's were made at some point. There are also half-lug N-frames. A half-lug 6" barrel would probably have a good balance.
Most people prefer the 4" or 3" for concealed carry or any kind of carry. A red dot sight resolves the short sight radius issue but does add to the overall bulk and limits holster compatibility. As long as I can conceal it with a big, heavy shirt or jacket, I like the longer-barreled gun. People who don't understand might think its ridiculous to carry such a huge revolver or that I must be convinced that it's so much more powerful than the kind of subcompact pistols that most people carry. I don't think that way. I just found what is easier for me to shoot well. It shouldn't be surprising to anyone that has actually shot guns and not just held them in their hands, that a big, heavy, long gun with an optic is easier to shoot well. I see it as an advantage and I don't like the idea of handicapping myself with something that is too small or difficult.
