I'd argue the assertion that the 686 is technically superior because it's stainless.
The stainless 686 will offer superior corrosion resistance.
The carbon 586 will offer superior wear resistance, in certain moving parts engagements.
Both should shoot comparably, allowing for differences between barrels & other dimensions inherent to any other gun or guns.
Shot little & rarely exposed to corrosive atrmospheres or agents, no "technical" superiority between the 586 & the 686, IN S&W'S STEEL FORMULATIONS, and IN OTHERWISE IDENTICAL OLDER VERSIONS WITHOUT MIMS OR LOCKS.
Decide which is more important to you.
The 686 will not wear out in a year, the 586 will not lose its bluing in a year.
As far as gas cutting goes, I've neither seen nor heard anything about stainless being more resistant to it than carbon steel, IN COMPARABLE S&W REVOLVERS IN GENERAL. Flame cutting is a function of heat and high-speed gas particle impact erosion, the slightly harder carbon should actually be at least fractionally more resistant than the stainless steel formulation.
Older pre-MIM & pre-lock 686 (in my opinion) is LIKELY to be better built overall than current 686s.
All work, none are junk.
I stick with the older 586.
Denis