With a ninja with all the dex increasing equips(no tincs!), you have 84 DEX, the katana gives -5 DEX, so you end up with 79 dex.
APS (attacks per second) = 1.5 + 6.5 * (79 / 75) = 8.3467
[(650)*(0.5+70/50)]*(8.3467*4.5)=46386.78525
If you take 4.5 secs to stack shots and 0.5 sec to run away, you can stack it so it inflicts an average: 46,386.78525 damage.
But, we don't know for how long the shots have before they disappear, I'm assuming(based on the comment above) it is five seconds.
It would be nice to stack this in front of a tomb boss(might have to paralyze it first though). Maybe a new challenge, all Doom katana ninjas tomb? :P