I believe that since multiple hits per is maxed at 8, dualwielding something in addition to Oclub or Kclub in mainhand would be a negative effect to zerging.
It depends on the delay of the other weapon. (As /NIN w/Suppa, you need to increase the average number of hits by at least a factor of 1.6 to break even with any sort of non-/DRG, non-/WAR option. I'm going to assume that you didn't bother putting DW+ on the add-on body, which obviously changes this number.)
Let's say that OClub and KClub have the same frequency distribution for each possible number of hits. Call the probabilities A through H. Your average number of hits single-wielding is (A+2B+3C+4D+5E+6F+7G+8H).
Dual-wielding, the average number of hits is:
(2*A^2 + 3*2AB + 4*(2AC + B^2) + 5*(2AD + 2BC) + 6*(2AE + 2BD + C^2) + 7*(2AF + 2BE + 2CD) + 8*(the sum of everything else, counting products of two different hit numbers twice))
(Yeah, being lazy on that last one because that sentence is shorter than listing all the terms.)
Assuming "occasionally attacks up to X times" is based on a "flip a coin, not necessarily fair; each time you get heads, that's an extra hit, flip again" model - which isn't very hard to implement, and (at "heads occurs ~45% of the time") matches up decently with observed 1A/2A/3As with Ridill:
* The "coin" gives heads roughly 40% of the time with KClub and OClub for the observed average of ~3.8 swings per round.
* This gives an average number of about 7.08 swings per round using both.
* The ratio here is about 1.855 - about 16% better than the change in delay from dual-wielding.
This 16% increase in hits needs to beat... oh, 6% in added haste? (I'll assume /DRG and using both the shield and the earring, and obviously less than 19% in other gear haste.) This lands at about 56% in haste before that point.
That figure (less than 56% in total haste,
not a real zerg
go /NIN) is probably wrong (I mean, the model in question is almost undoubtedly simpler than whatever baroque monstrosity SE decided to implement) but it's at least probably in the right ballpark.