For a hellrack, ias makes a big difference. Looking at my damage calc spreadsheet, with just the base mods on the hellrack (i.e. 20% ias), and comparing it to upgraded buriza and a Windforce, it looks like this:
Buriza (upg) (assume lvl 90 for +dmg/lvl) - 80% ias base
409.77 dmg/attack
14 frames/attack -> 1.7 attacks/sec -> 696.61 dmg/sec
Hellrack - 20% ias base
801.15 dmg/attack
18 frames/attack -> 1.3 attacks/sec -> 1041.50 dmg/sec
Windforce - 20% ias base
277.125 dmg/attack
13 frames/attack -> 1.9 att/sec -> 526.54 dmg/sec
Now lets consider adding ias – With 20% ias beyond what the weapon comes equipped with, it drops the buriza to 13fpa and the Hellrack to 16fpa, with windforce in the lead with 11 fpa.
20% extra ias
Buriza (upg, clvl90): 778.56 dmg/sec
Hellrack: 1201.73 dmg/sec
Windforce: 609.68 dmg/sec
But the upgrade to 40%ias doesn’t net the buriza anything, whereas hellrack sheds another frame, down to 15fpa. Windforce only drops one frame to 11fpa.
40% extra ias
Buriza (upg, clvl90): 778.56 dmg/sec
Hellrack: 1281.84 dmg/sec
Windforce: 692.81 dmg/sec
Now, this ias doesn’t have to come from the two sockets in the hellrack of course, it could come from gloves, amulets, whatever. However, lets say you already have a pair of 20% ias gloves, bringing your total to 60% extra ias beyond base. Let’s also say that you have the items to give you 60% extra ias with buriza and windforce (perhaps a Shael in the weapon and a Highlords Wrath, for example). This nets both buriza and hellrack a slimmer profile by one frame, with buriza at 12fpa and hellrack at 14 (incidentally what buriza starts out at). Windforce doesn’t net anything (ouch!) until 69% ias above what comes equipped.
60% extra ias
Buriza (upg, clvl90): 819.54dmg/sec
Hellrack: 1361.96 dmg/sec
Windforce: 692.81 dmg/sec
Hellrack still emerges the winner (AND it’s of note that 40% ias can come from sockets in the hellrack itself. Using the gloves above and a highlords with hellrack gets you 80% extra ias, dropping yet another frame from your attack animation). This just proves that the weapons that come equipped with large elemental damages are in general better at dishing it out, even though not all of your damage is leech-able. It’s a wonder that anyone wants the poor old Windforce, considering that even a non-upgraded Buriza dishes out more damage until you hit 40% extra ias (and it takes the lead back at 60%, until wf gets another big break at 69%).
Now to be fair, this calculation is very primitive – it only considers the average weapon damage per attack, without any strength/dex modifiers or monster resistances. Still, it says a lot for putting 2 shaels in your hellrack, since it raises your damage output by 240 dmg/sec. Putting 2 Ohms for 100% ED will instead only raise it by 80 dmg/sec. This is the same reasoning for why my Holy Freeze pally has a shaeled azurewrath and 15% ias jewels in his Gaze and Guardian Angel – doing so dropped me one frame on my zeal, which did more for my damage due to the massive elemental damage on Azurewrath and the more massive Holy Freeze damage than putting an Ohm in the Azure and 40% ED jewels in the helm/armor would have.
A pair of 40ED/15% ias jewels would net you 80%ED/30%ias from the hellrack, giving you a 15 frame attack with a damage output of 136.56 dmg/sec. This beats two shaels, but is also grossly more expensive (and can be made up for by 20% ias gloves, though if you’re going to have them and dual 40/15’s it’d drop you to 14 frames and 1445.60 dmg/sec, so perhaps that’s a less convincing point). Perhaps this explains the reason 40/15 jewels are so expensive.
