I've heard in the past that dual-wielding with a KC is not the best idea, because it will drop your delay and the extra swings will be nullified by the 8-hit per-round cap. A friend and I have been debating this back and forth for some time, so I decided to finally investigate.
First thing I noticed that I haven't seen before is otherwiki (bottom of the page) has found via studio gobli that the KC breaks down to:
5:15:25:25:15:10:3:2 percent chance. That's 5% for 1 swing up to 2% for 8 swings. Average 3.82.
We've known for a while that the Ridill breaks down to 30:50:20, and otherwiki says (but does not source) M. Kris at 10:80:10 new testing shows a likely M.Kris breakdown of 30:60:10
So applying the percentage chances to eachother, it breaks down that a dual-wielding Ridill/KC breaks down to
0*:1.5:7:16:23:22:15.5:15**
And for KC/M.Kris
0*:1.5:7.5:17:24:22:14.5:13.5*
*Dual-wielding, can't only swing once
**The 8-swing cap means that 8-11 all count for 8, it separates out to 8.9:4.1:1.6:0.4 for KC/Ridill and 8.4:3.4:1.5:.2 for KC/M.kris
The delay totals are
KC: 264
Ridill/KC: 425(400 w/ suppa, 385 w/ suppa & Nuevo Dualwield)
KC/M.kris: 387(364 w/ suppa, 351 w/ suppa & Nuevo Dualwield)
I am unsure, but believe that means KC will be 1.6098484... swings for every Ridill/KC(1.515151... w/suppa 1.458333...w/ suppa & Nuevo Dualwield) and 1.4659090... for KC/M.kris(1.3787878... w/ suppa 1.3295454...w/ suppa & Nuevo Dualwield).
Assuming you have a Suppa:
In order for the KC/M.Kris to be better it must have an average of 5.57 swings, or 46% better. In order for the Ridill/KC to be better it must have an average of 6.11, or 60%, better.
(If you have a Nuevo-augmented with Dualwield it becomes 5.04 swings for kris-combo, 32%/5.57 swings, 45% for Ridill)
Thanks to formulas from Raen Ryong below we can find that:
Ridill/KC gets an average of 5.635 per round
KC/M.Kris gets an average of 5.55
Therefore, on number of swings alone:
A KC will average half a swing better in the same amount of time than a Ridill/KC.
A KC will average a very slight fraction better than a KC/M.Kris
However those numbers assume no dualwield gear, adding in a suppa means the KC/M.Kris becomes a touch better, adding both a suppa and Augmented Nuevo pushes it to about half of a swing. Ridill still loses with those extra.
It's the smallest of direct upgrades, and it does not take into account the bonuses you can get from /drg and/or the 30 HP shield.
What's unknown is both the Studio-Gobli numbers, though they're usually trusted.
If my math's wrong feel free to tear in, I'm pretty sure of it though.