The slower your weapon is, the bigger benefit it gets with Attack Speed.
1.0 swing/s = 1.0 speed -> 30% ias -> 0.7 0.3 decrease
1.5 swing/s = 0.5 speed -> 30% ias -> 0.35 0.15 decrease.
(of course the difference between them will remain constant, but at this point, weapon damage is more interesting imho.)
The difference remaining constant is what's important. Would you take a .1 attacks per second weapon with 50 more dps than a 1.5 attacks per second weapon, just because your IAS rings and necklace provide a larger per second gain? no. The percentage gain is the same, so it's really NOT a gain. The DPS gain is constant and does not change. So, again, two weapons one with IAS one without, and otherwise equal, the IAS weapon is superior for the vast majority of applications (including kiting which, let's face it, is the REALLY important application). This is like the inverse of armor calculations, where gains look smaller but remain linear - yeah you add less attacks per second to the faster weapon, but you add the same dps.
What buff settings should I try out?
The common barb builds are all Nerves of Steel/Tough as Nails/Superstition passive, War Cry/Impunity for your buff. Those are the only ones that affect your stats.
Otherwise, Revenge/provocation is obvious and 100% required, Frenzy sidearm procs more life on hit and does the most dps in almost all situations. You occasionally see slight variation in other abilities but it's PRETTY typical to have:
Frenzy/sidearm, Furious charge/Dreadnaught, Threatening Roar/(Falter or Grim Harvest), War Cry/Impunity, Revenge/Provocation, Wrath of the Berserker/Insanity.
Threatening and Wrath are the most likely not to be in someone's build, threatening you can drop for quake when you can handle mobs decently, but when you're 'fresh' to an act it's really good to have the -damage debuff.
Wrath though it may not look it is a HUGE defensive cooldown for elites/champs, since it gives you immunity to CC you can use it to break a fear/freeze/whatever and burn a mob down, making the rest vastly easier. Charge is both a quality heal (8% per mob), an escape/movement tool, AND a CC immunity. You can't break CC (except jailer) with it, but you can AVOID most with it. Like charging when freeze bombs blow up will not freeze you, even if you're 'inside' them when you're charging by them. It can get you through arcane beams with little damage, etc. It's just fantastic. Timing is hard, but that's good it makes it like a skillshot type deal.