Is using a Epic SoS a lot better than a Lit II? Yes! Does the Rage spell add to DPS? Yes! Is getting an Epic SoS a bigger DPS differentiator than getting Rage cast on you? Yes! How much more important is it? Ummm....
Even being a historical "number cruncher", I found myself surprised a couple weeks back when comparing damage contributions of Frenzy to some other elements. So I thought I'd go through a little exercise to itemize the damage contributions from a bunch of different factors, so I could get a better sense of which pieces were of critical importance, and which were just "nice to haves".
So, I started with a template of a "max equipment, max STR, max DPS" Half-Orc Barbarian 20, assuming:
Starting 20 STR, all level-ups in STR, +4 STR tome
All available damage-scaling enhancements
Full THF line, iCrit Slashing
Epic Sword of Shadows
Epic Bloodstone
Madstone Boots
Claw Set
FB and Ravager ToD sets
Titan's Grip
All available STR pots
Haste, Rage, max-Warchanter songs, Prayer spells
Guild ship buffs
I then compared this scenario's DPS (vs. 0 fortification opponents, but without sneak attack) vs. the same scenario with one element removed, to get a percentage differential on an item by item basis. The numbers aren't cumulative -- for example, when you see "No Haste -9.8%" and then "No Frenzy -3.9%", you can imagine me removing Haste from the baseline, comparing, and *then* adding haste back in, and removing Frenzy.
The numbers are interesting -- some things that were expected, and some surprises.
PA off -15.5%
No Barb Rage -14.9%
Replace SoS with +5 Holy Burst/Icy Burst/Pure Good Falchion -14.2%
No Imp. Crit Slashing -12.2%
Replace SoS with Lit II -11.3%
No Death Frenzy -10.8%
No THF feats -10.4%
No Haste -9.8%
No PA enhancements -8.4%
No Bard Songs -6.3%
No capstone -5%
No Ravager ToD set -4.9%
No Frenzy -3.9%
No Bloodstone -3.5%
No Titan's Grip -3.1%
No STR pots -3.1%
No FB ToD set -2.8%
No Horc two-handed damage enhancements -2.8%
No STR Tome -2.1%
No Madstone -2.1%
Non-epic Bloodstone -1.4%
No Claw Set -1.4%
No Rage Spell -1%
Replace +4 STR tome with +2 STR tome -1%
No Greater Weapon Aptitude -0.46%
Some quick observations: a Lit II is only marginally better than a nice Ice-games-crafted DPS weapon. (In fact, if you manage to craft a Holy Burst/Greater Bane and don't need to worry about DR, it's *better* than a Lit II once you Icy it up...) The differential between Epic SoS and everything else, though, is still pretty amazing.
The difference between using an Epic Bloodstone, and not having any Seeker items at all, is a measly 3.5%. In fact, after you resign yourself to not having an Epic SoS, a lot of most sought-after equipment options are pretty marginal: Epic Bloodstone, both ToD sets, Titan's Grip, Madstone boots -- nothing breaks over a 5% difference.
Also, in terms of buffs: Haste, Songs are pretty critical. The Rage spell is so negligable as to wonder if it's a waste of time for people to stand still waiting for it!
Here are some interesting little "mini-scenarios":
“The Poor Man” (-35.8) : This is the "no good equipment" scenario, taking away all equipment and tomes, only granting the Risia-crafted Falchion.
“The Forgetful Barb” (-29.6) : This is the "bad player" scenario -- the guy who is constantly forgetting to use his abilities; no Rage, no Frenzy, no Death Frenzy
“The Bad Build” (-43.1) : This is the "bad build" scenario (duh!) -- leaving out Power Attack, the THF feats, and Imp. Crit
Bad Player >> Bad Build? (just kidding... mostly)
I might do other flavors of this in the future: Kensai 20, Assassin 20 seem like they'd be interesting and slightly different...