My LGS's website (finally) has the Model 686, 6 round, 4.125" barrel:
Model 686 | Smith & Wesson
My only concerns are that I'd like a 7 shot and that this one seems a little on the light side, at 39.7 oz, which concerns me about recoil reduction, because I wanted one in the higher 40s oz range. Thoughts?
I think you're thinking too hard about this. But if you're really hung up on the weight, why not the 6" model? That adds about 5 oz to the weight of the gun.
Subjectively, I've found that felt recoil is a function of more than the weight of the gun and the barrel length. To wit: I have a Model 60 Pro Series (J frame) with a 3" barrel that feels like it has less felt recoil than my substantially-heavier K-framed Model 65 (which also has a 3" barrel). My guess is that the grip shape (and probably the grips themselves) on the 60 fit my hand better than the 65, but I haven't really cared enough to make a scientific study of it.
For what little it's worth: the best revolver that I own for managing felt recoil is my X frame 460 XVR. .45 Colt rounds in it feel like shooting .22 out of a Model 617. But it's a beast of a revolver at about 72 ounces, and it has a large rubber grip to boot ... so you take the good with the bad there.
Over the years I've learned that fit is a lot more important than the numbers. The easiest example I can give here are the semi-autos from Springfield Armory. They're good guns by any measure, but the ergonomics of the three that I've owned just haven't worked for my body geometry. The M&P line is a much better fit for me, but Glock seems to work the best. We can argue endlessly which gun is better on paper, but at the end of the day the Glock fits my hand the best, and (for me) that translates to tighter groups and better shooting.
I've also found that as my shooting has improved over time, my taste in guns has also changed. 10 years ago I hated the 1911 platform, and couldn't hit the broad side of a barn with one. Now, it's the gun I'm shooting the most at the range.
Long story short: don't get too bent over a few ounces. There are a lot of other forces at work—some that you can control, and some that you can't—that will ultimately decide whether a 686 is the right gun for you.
Mike