Consider 4 damage ranges: None, Regular Max, and True Max.
The damage increments for these ranges are as follows:

None: 100% (No damage added on)
Regular Max: 124% (the 6 stages of damage you can normally get to)
True Max: 225% (Deadly Shadow Cloak, an attack orb, and 6 stages = 1.4 * 1.3 * 1.24)

These are applied to the base damage of weapons, prior to the defense of a monster being subtracted from them. Because of this, the "best" sword for the job depends entirely on how much damage bonus you've got going on. Lets have a look at some noteworthy weapons by approximate base damage, and the consequences of this base damage:

Combuster/Glacius/Voltedge: (First swing / third swing / charge / splosion)
EDIT: The wiki has wrong data somewhere; I assume that it is correct only on the "strong" damage.
Normal Component = 231 / 276 / 392 / 177
Special Component = 231 / 276 / 392 / 177
Grand Total = 462 / 552 / 784 / 354
Combos after deadly shadow cloak = 2

Total damage, best case (2 combos after deadly shadow on true max) = 6262
Total damage, just charge hits = 1591

Total damage, normal max damage (2 combos) = 2811

Total damage, no buffs (2 combos) = 1932

Cold Iron Vanquisher: (First swing / third swing / charge swings )
Normal Component = 350 / 402 / 524
Damage of 3 charge swings in total = 1572
Combos after deadly shadow cloak = 2

Total damage, charge case (1 charge after deadly shadow on true max) = 3045
Total damage, best case (2 combos after deadly shadow on true max) = 3975

Total damage, max damage = 1457

Total damage vs undead, no extra buffs = 1268

Dread Venom Striker: (First swing / ghost swing / finisher or charge)
Normal Component = 272 / 231 / 318
Grand Total per slash = 503 / 549
Combos after deadly shadow cloak = 2

Total damage, best case (2 combos after deadly shadow on true max) = 8244

Total damage, max damage (2 combos, regular max damage) = 3071

No damage bonus, 2 combos = 1842

So as you can see.....

Cold Iron Vanquisher might appear to be stronger whenever you compare it to combuster's charge, but in the end, true damage wins out and you'd be better off with a brandish or cutter line weapon, unless you refuse to use damage buffs and still manage to have charge time reduction for some reason. Note that while on a combo to combo basis, cutter lines outdamage brandish lines, the brandish lines have a much better charge attack and don't require ultra close range + constant spamming of attacks to work, enabling them to generally outperform the dread venom striker.

Another interesting thing is that warmaster rocket hammer's normal combo works much better than cold iron vanquisher, regardless of damage buffs. At a glance, it does 1466 damage per combo with no buffs applied.

Note: These damage values are hypothetical, using the accepted formula for damage, which can be found on this page of the wiki- http://wiki.spiralknights.com/Defense All damage values etc. were found and calculated also through the wiki, and I did round numbers a good deal to make them neater while still getting my point across.

By my math, the "field of view" would hit for a grand total of 4964, if it hit all 3 times under the optimal scenario.

It should seem that the numbers on the wiki are incorrect for combuster's damage. Guessing that the numbers for against construct and undead are correct, we get that combuster's single charge would do around 1591 at most without taking into account any explosions. This is significantly worse than what 2 combos would do- 6262 damage. Why 2 combos? Because you only have that amount of time to get in those hits at the end of a deadly shadow cloak, which speeds up your attacks to let you land it all.

I'll edit the post above because of the wrong data on the wiki.

EDIT: And done. I redid a good portion of the math, to illustrate my point- that the "best" sword for the task depends on how much damage bonus you have.

The wiki claims that combuster has the same damage numbers vs "undead and construct" as it does vs "fiends and slimes", which I find hard to believe.

As for the post, I've revised it to have all of the necessary damage numbers for the three swords, excluding warmaster rocket hammer. I also put out a disclaimer, as I have not actually tested these in person, but since as you said no one has, I did the calculations based on the defense formula to come to some sort of conclusion without wasting massive portions of my life going down to D28. I say D28, because I used the upper end of the wiki's numbers for the sake of continuity. If someone wants to go down to D28 and record real numbers, I'm sure they'll be somewhat different from the ones I've came up with, as mine are just calculated estimates.

I don't know the health of the mobs either, but I don't think that it would matter as much as one might think since other weapons can easily fill in the gaps with other less damaging weapons and dealing more damage wards off the effects of healers. It would still be nice to know, I suppose.

I would also expect all of this to work out differently, as 2 combos = 1 charge is probably not exactly the best standard, except for in the original case that I brought up- after deadly shadow cloak. I kept it to that ratio purely because I wanted all of the numbers to be easily comparable.

I mostly brought it up for the sake of seeing what happens as you increase the damage multiplier higher and higher. The same general trends should be visible with most extremly high damage increases, like attack orb + drakon boost, drakon + mask boost, or even just attack orb boost. If you are playing with DVS, you would want to stack as much damage as often as possible, so you'd end up with a wide variety of these situations as you cornered+killed mobs.

I'm gonna ignore maths and most of what the OP contains completely and say WRH. It's super easy to land the first hit+three dash hits on both of these targets and the mobility is pretty useful for dodging and redirecting them if you can't kill them in just a combo or so. Provided you aren't in a big party and/or on elite, you can also use WRH to dispose of the Howlitzer when it becomes homing if you learn the timing and positioning required for hitting the head properly.

im not testing but ill be watching this for any hammer data

FoV > all

until it sets you on fire

"Dread Venom Striker: (First swing / ghost swing / finisher or charge)
Normal Component = 272 / 231 / 318
Grand Total per slash = 503 / 549
Combos after deadly shadow cloak = 2

I assume consistent DVS switch would boost these numbers.

"I don't know what you mean by consistent switch"

I think he means like alchemer switching. Doing it continuously without mistakes.

You don't need two weapons to switch attack, it just makes it a bit easier if you don't have to switch twice.