Well done Nibs, my numbers match yours now for the old skill, now that I took out multi-attack procs adjusting the quad chance. Now...as for the new skill, here are the numbers, as always, skills @ 100:
No multi-attack gear(to increase DA chance over 20%):
Base Single: 80%
Base Double: 20%
Final Single: 80%*90% = 72%
Final Double = 20%*90% = 18%
Quad Chance = 80%*10% = 8%
Quint Chance = 20%*10% = 2%
Old DPS = ,8 + .2*2 = 1.2
New DPS = .72 + .18*2 + .08*4 + .02*5 = 1.5
DPS increase = 1.5/1.2 = 1.25, or 25%(when mob/player is at full HP)
Assuming this works the "opposite" way of vengeance, giving 0% quad chance when enemy has 1hp left, the bonus would roughly be cut in 1/2, so ~12.5% dps increase. More on that later!
Here are a few more combos:
Thraki+2xLoDs: 1.607/1.307 = 1.2295 = 22.95% increase, cut in 1/2 is 11.475% DPS increase
Thraki+Runed Flurry: 1.6081/1.3081 = 1.2293 = 22.93% increase, cut in 1/2 is 11.47% DPS increase
Thraki+DW DA Piercers: 1.7238/1.4238 = 1.2107 = 21.07% increase, cut in 1/2 is 10.535% DPS increase
All combos are between 10.5% and 12.5% boosts, assuming a linear progression in the reduction to quad chance.
You'll notice with teh way the new skill works, basically you have a 10% chance to add 3 attacks, so number of attacks per swing always increases by 0.3. Makes it pretty easy to calc, and also pretty even across all builds, good job Glitch on teh balance to this one!
Side note for teh people who really care way too much like myself:
When fighting mobs with large amounts of HP, the DPS boost is greater at the start of fight, and less near the end. Because of the extra attacks at the beginning of the fight, putting the mobs health below where it "should" be, the chance for quads is reduced slightly faster than a linear progression, causing the actual DPS boost to be less than the approximated 50% that is used in teh above calcs. For example, in a fight taht takes 1000 hits to kill the mob, instead of the 12.5% DPS boost, it is actually ~12.05%. A huge loss, I know, but still a loss!
TL ; DR New skill gives 10.5-12.5% DPS boost to melees @ 100. YAY!!!