IAS benefits low mana spells such as Splinters & Ghost Bomb in particular bcos u wont run out of mana no matter how fast ur attacks are. While Splinters is good for single target & GB for a group of mobs bcos of a small AoE, damage wise when crits is concerned (at high mp critical hits is what matters) both have low weapon dmg multiplier which in turn result in lower crits (even when u use high base damage 2h wpn such as Skorn).
I wont try to give a detailed complicated dmg calculation formula but just a simple maths will suffice:
Splinters: 3 x 60% wpn damage
Ghost Bombs: 110% wpn dmg + 30% wpn dmg (AoE 20 yrds)
Acid Rain: 115% wpn dmg + 150% wpn dmg (AoE 24 yrds & DoT means 50% every 1 sec for 3 sec)
Zombie Bears: 3 x 236% wpn dmg for a whopping total 708% wpn dmg!!!
Using a 1k dps EF with OS (max of 100% CD) as a baseline.. we're talking per hit and will be disregardng ias for now:
Splinter: normal dmg = 3 x 600, crit dmg = 3 x 1200
GB: normal dmg = 1.1k + 300 (AoE), crit dmg = 2.2k + 600 (AoE)
AR: normal dmg = 1.15k + 1.5k (AoE over 3 secs), crit dmg = 2.3k + 3k (AoE over 3 secs)
Bears: normal dmg = 3 x 2.36k, crit dmg = 3 x 4.72k
Its clear that Bears is the obvious winner if u dont take mana into account. To clear a large pack of white mobs at lower mp AR beats GB hands down. Both Bears & AR are huge mana spells so having a higher IAS means u run out of mana faster.. 0 mana = 0 dmg
1h + mojo VS 2h
I do MF runs using Sun Keeper with OS + Mojo & Uber/Key runs using LS Skorn with OS. Both have about same character sheet dps 90-93k. However i can see from my runs that crits with bears using 1h+mojo range arnd 100-300k while when using 2h crits are 250-500k range.
Crit dmg benefit wpn with high base dmg .. the closer the gap between min & max dmg the better.
EF + avg dmg of mojo (200-250) .. even EF max dmg cannot go over Skorn's min dmg.
EF = (1.4 aps + max 100% CD + OS), Skorn (1 aps + max 200% CD + OS) ... would i prefer 0.4 more attack per sec @ 100% more CD? obviously more CD wins ... and dont forget u can get max 6% LS on Skorn & only max 3% LS on EF (which wont be enuff to counter RD).
My current setup of 12xx dps 5.6% LS Skorn enables me to spam bears continuously while gaining back life (even on RD packs i wont lose life). I manage mana by having Blood Ritual Passive, main attack of Posion Dart/Spine Dart for quick mana regen (29 mana per target hit). Keep left click pressed and spamming Bears rarely make me go OOM. I hv Hex on to disable any mobs that get close to me ..in cases of descrator pool, arcane sentry etc, i just SW away (HG make sure i hv mana when SW is over) to reposition myself and continue spamming... if i get focused on mortar @ any ranged attacks that depletes my health fast, a few AR spam will get me back to max health. I mow down pack of mobs, even RD packs faster with this setup .... crits are so high that as long as i dont get 1-shot i will survive (higher crit = more life gained from LS).
I wont argue that using best/optimum gears, a 1h+ mojo setup is superior (more vit, more regen, more crit from mojo) but good luck getting that elusive 1xxx dps Carving Knife with OS or a perfectly rolled EF/rare ceremonial knife with high dps + 100% base CD + OS.
For now going Skorn is the most affordable option for me to deal with higher MP lvl and RD packs. I only hv to invest in 1 instead of 2 (1h wpn + mojo) gear. I got my Skorn at a bargain price of 15m and its a pretty good investment i hv to say.
Dont take my word for it .. go out and test it yourself and see the difference (keep a close watch on the yellow figures on mobs & notice how fast u clear tough packs). If u cant afford a LS Skorn .. get a rare 2h with at least 5.5% LS + higher base CD from ur current 1h + OS (if ur 1h wpn hv OS).. get as close dps as ur 1h+mojo dps total setup for comparison sake.
No worries, tyt bro.
Its a 5.6% LS Skorn and it solves my RD problem

what do u mean by Bear is capped at 7%? What 7%? Care to elaborate or share a blue post (blizz's mod) post in d3 forum regarding this?
I used to deal with RD using same technique when using my EF .. Bears only when SW is up + RoT in between ... trust me on higher mp u will be spending so much time to take down even 1 pack of RD (let alone 2 RD packs close together).
B4 i got my LS Skorn i stacked LoH so high so that i only hv to spam few AR to gain back life to maximum from a near death situation. Now that i hv 5.6% LS i hv started to lose my LoH gears. Alrdy changed my Ouroboros ammy with a rare ammy that boost my dps/ehp (lost 400+ LoH). Next to go is my Jousting Mail pants (400+ LoH) replaced by Inna Temperance (to get more dps as LS scale better with higher dps). I probably keep arnd 400-500 LoH (from rings) for Acid Rain spam to get back life fast.