Pardon me while I stir the 'puddin'. The seven shot 686+ began with the -4 in 1995. The OD of the cylinder is the same, as the frame's opening is the same. The spacing of the chambers is closer, of course, but recall that the S&W frames & cylinders were forged and heat treated, rather than cast as some others. Additionally, the 60 degree vs 72 degree rotation per trigger squeeze requires a slightly different hand - and has a different feel, however slight. Remember that the cylinder has an addiotional 'hole' detracting from it's mass, so the shorter hand's loss of mechanical advantage won't be as noticeable. They 'break in' to a great trigger. As I like the 66's look, I jumped on a similar 5" half lug 686+ stocking dealer exclusive in '04. The full lug normal 686/686+ didn't look good to me. I like partial lugs! Side by side, my 6" 66 and 5" h-l 686+ do look very similar - even down to now wearing the same stocks (Ahrends) and front sights (HiViz). If I am shooting a 5-plate 'steel plate challenge', that seven rounds is good insurance (The shoot-offs have a sixth stop shot... nice to have an 'extra' round!).
New 4" 686/686+ run $519-$539 locally, while the 66's replacement, the new 4" 620, is $489. It is the same L-frame as the 686+ - with the same 7-shot cylinder - and the 66's nice half-lug barrel, albeit the modern enhanced two piece style. When I get ready for a 4", that'll be it - it can even 'share' my 686+'s HKS 587 speedloaders. I started buying S&W new in '02, so most of mine have 'The Lock' and MIM parts, neither of which have been a problem here. In fact, my troublesome S&W's were all older models, now, thankfully, gone, their 'value' used to buy new current ones. YMMV.
Stainz
PS This is post #619 for me... the 619 is a fixed sight holster version of the 620 - a 65 replacement, actually.