I wonder how much % chance to hit people actually gain from amethysts, it seems negligible compared to 1000 or so attack rating you get from various set bonuses.
Of course this can be easily tested and the difference in chance directly translates to % more total damage.
For pvm nothing beats angelic barb anyway and this build greatly benefits from a perfect skull socket.
However an "extra gold" barbarian might be better off with a mana/dual-leech ring and a PA-martel, rather than a dual-leech martel and an attack rating ring.
Bottom line is: even if you have great leech rings and +2 skills amulets, then extra leach will still provide some comfort to your pvm play and a lot of options when it comes to equipment.
With leech problems out of the way you can use +15 strength / SoJ / or angelic combo to increase your damage. An amethyst socket hardly will make any noticeable difference.
A skull socket becomes entirely useless for pvp however.
Why can't some people find peace with the "2 hand weapon

skull , 1 hand weapon ---> amethyst" rule... i don't know, probably because of executioner swords.