Well, things i've discovered:
No, u cant cast the skill with swords, but yes, u can swap weaps before it ends casting.
Second, it actually only depends on WEAP WEIGHT. I tried wearing a bsb, and not wearing it (100 atk its a high diff...) and the skill dmg was EXACTLY THE SAME. Also, using a triden and a pike, wich have like 90 atk diff between each other, but only 20 weith dif, and the dif was minimal (2.1 with the trident, and 1.8 with the pike).
Third, weap upgrades at lvl 4 give a HUGE diference. I made 5.8k with a +4 brionac (120 weight, lvl 4) against a 5.1k with a +7 very very very strong lance (250 w8, lvl 3) and finally 4.9k with a +0 lance. So, +4 upgrade at lvl 4 beated even a +3 up of a lvl 3 and a 120 weight diff.
Elemental endow works exactly as rms says (tried with the same monster, with an elemental weaknes of 150% and got the perfect extra dmg)
I think percent cards also work fine.
So in conclusion, the importance to get more dmg would be:
amounth and lvl of upgrades > weight > atk(skill doesnt use it) + cards and element. So i guess the best is to get a heavy lvl 4 weap, and try to upgrade it as much as posible
[Modify: Also dont forget the size dmg modifier]
