The ideal 686+ (you said 7 rounds so it is a 686+) is the one I am using for the particular use of the day.
My 4" 686+ in its custom holster is the one that goes to the feral hog fields with me.
My 3" 686+ is presently my bedside gun. Why? Mostly because I think it balances better than the 2.5" 686+ that it replaced and because, at zero-dark-thirty, as much as I like those pretty rosewood stocks, if I am in
OMG-SOMEONE-IS-IN-THE-HOUSE mode I don't want my sleepy hands sliding on that polished wood, I want a solid grip and I want it
NOW!.
There is nothing particularly special or different in these guns when it comes to shooting. Recoil is more or less negligible, even with full house loads. Accuracy varies a little due to barrel length but since most of the shooting gets done at an indoor range the distance where accuracy could change long barrel to short barrel doesn't really exist.
So, please note that a 6" barrel is not in the offing for me. Why? Because I have a 6" 586, it is deadly accurate at long range, just not so easy to tote around so I don't even have a proper holster for it. I just carry it in a gun rug and if I want to use it I take it out and let'r'rip. So a 6" 686+ is just not needed (I know, need is not what counts, but I have the one 6" so I don't want any others presently, either.

)
Scientific? I was at a close quarters pistol craft class and I ran out of 9mm ammunition (long story as to why; twas not my fault!)so they let me switch to the 4" 686+. I devastated the targets, including a moving combat target. Nothing like a 4" barreled combat revolver!
That's as scientific as I can get.