haven't read all comments, but i have made some calculations as well and came to the conclusion that for
hammerdinInsight GT / Andy(ias-jooled)
Forti is
better.
I tried to follow your calculation but I have this problem:
Damage with Concentration aura per hit
FortiQuote
Damage : 3294 - 9384 (6339 Avg.)
TreacheryQuote
Damage : 3059 - 8715 (5887 Avg.)
That's
7.7% more for forti.
With 239 Str, 570ed Conv aura, 250ed Might Aura
A Simple Calculation Leads to
(3.39 + 3 + 5.7 + 2.5)/(3.39 + 5.7 + 2.5) = 126% ->
26% DamageboostWithout Conc and/or Might aura the Boost is even bigger!
I Think your calculation has some flaws.
By the way, CA/CV has more dps, since it has a break point at exactly 35 ias, with you just reach.
Nevertheless If you use a CB-weapon, treachery can be better, since you have higher weapon speed. The question what is better depends on the monster you fight. I use Infinity Tresher/Treachery/Andy-jeweled for my summoner Nec because of that. He kills bosses like Baal quite fast.