Dual Blade questions and worries

What should I max now then for my last skill? I figured Tornado Spin would be best for max efficiency with Bloody Storm and Flying Assaulter, that just means Ill have to pick up the rest of Shadow Resistance later in 3rd job.

If you follow what I gave you, you will have maxed tornado spin within 3rd job. Most mobs in your early 3rd job days dies so easily anyways you don't need tornado spin (its weaker than bloody storm anyways) much at all. Some people like spamming Upperstab in 3rd job days instead of using Flying Assaulter + Bloody Storm or Tornado Spin. Maxing Tornado Spin before 3rd job is useless really and you should be saving SP instead to your 3rd job skills. Flying Assaulter + Tornado Spin is usually best combined with Upperstab once you send all your mobs to the corner but usually by then they're already almost all dead so theres no point in rushing them all to the corner.

How big is the difference in DPM between spamming Upper Stab and Chains of Hell at bosses? To be completely honest, I dont like spamming Upper Stab mindlessly :x its not exactly the coolest looking skill to watch, and spamming it makes the dual blade look like a spazz on a sugar high. I was under the impression that the highest DPM for a dual blade pre-big bang was chains of hell, so what is the DPM difference between the two at a boss like zakum or HT?

I'm not a math expert, so I can't give you any DPM numbers, someone else can do that. In the time frame that you pull off 1 CoH its about the same as using 3-4 US. DPM wise if all are ideal situations, CoH vs US is nearly the same except that CoH requires more effort if you want the best DPM. That means CoH can't be spammed 24/7 and you must always be in dark sight at all times to use CoH and you must keep track of times when your dark sight doesn't come off thanks to advanced DS for the best possible DPM with CoH. If you're too lazy to do any of that or can't keep up with the timing, just don't bother with using it at bosses if you ask me. The only thing its good for is the invincibility frames while in animation. Its already a pain in the ass to use at any bosses that dispels at you.

Answers are in red.