If you have been doing your research like you said you have, then I've imagined you've read multiple comments about how the extra 10 damage levi deals over CiV is completely negligible, as it would still take the same amount of strikes to kill a monster. The same can be said with CiV on an undead over leviathan.

The only real difference I find with the two blades is with the charge attacks.
From what I know, both blades have the potential to hit up to 2-3 times on the charge.
In cases of immobile mobs (frozen or puppies), when you are directly next to the enemy, CiV will hit thrice, as for for leviathan I'd assume the same but I haven't got one so I might be wrong. (Though I'm quite confident it is the case)
As far as i've seen against mobile mobs, levi's charge will almost never hit for more then once, where as CiV could be consistently hitting twice.
And just to add, I don't think I've seen my CiV hit for thrice on a moving mob.

Also, I think it is general consensus that leviathans knock-back is quite bothersome to the party.
I've seen many situations where lumbers would be flying towards people mid strike and do some hurting.

Back when I first started, I chose CiV over leviathan because of the looks.
I didn't care if CiV was worse, I'd make it up with skill (lol), but since acquiring CiV I have never considered leviathan to be better, rather I'd imagine CiV was better due to the charge. Then again, I've never owned a leviathan. (But it's the same as a calibur isn't it?)

Lastly, I don't think you should consider using radiant silver mail, there are better alternatives if you don't want to go vog or skolver. Namely magic cloak line and

While the damage difference is smaller the lower the level, also the monster's health, since the entire game works like that... Also as far as i know the bonus damage from radiant, will be added first to your existing bonus, and then it will be applied to the sword's damage, it won't add it over your modified sword damage, so it won't make a difference between the two swords. Damage may be important for number crunching but it is not a deciding factor for the average player. As a leviathan user I can't imagine how would it help me to unleash a charge that doesn't do enough knockback, as the main use of the charge is to hit and run, except you can't run so you push the enemies instead, that being said I would find it useful in some instances, but not most. CIV's knockback may or may not be enough but its users apparently manage so its cool. The same way a CIV user can work his way around a levi user can as well, before unleashing your charge look at the battlefield and think where its best to push the enemy. Sometimes you'll fail but that will be because of a genuine mistake. Leviathan will hit only once on mobile enemies, and you may learn how to hit twice and even thrice as you play, even on an open field (common with gremlins), but even after learning it may be difficult to pull off, it hits three times with Shivermist unless you push them to much on the first hit. I suggest you compare the knockback of both and decide which you like more, and if you want civ because it looks cooler then go ahead forget about numbers.

The calibur line charge will rarely save you during any status affliction, during freeze, if you you got frozen, you are probably about to be hit again before you charge, stun makes all your animations so damned slow you are better not attacking at all and just running away until it wears off, the charge even if you get to unleash it will take so long it will let enemies you missed hit you with ease. During shock it will not let you charge, same as fire, with curse you cant attack, poison is the only one left but your charge will be too weakened to unleash, only useful on emergencies, you better wait until the timer runs.

Fire is the only status that covers wide areas thanks to the flamethrower attacks, the others are easier to dodge/shield. Fire is nice to max out, your owlite will help you some even if you dont max out. Having half of each defense is okay if you wont spend a lot and want a single set, you'll have to play careful of not getting hit as always.

cant answer for that, but that knockback seems okay, and its enough to bother teammates I believe. The knockback depends on your impulse and the enemy impulse at the moment of contact and how close the enemy is to your characters center doing that, with leviathan you can send a lumber to the other side of the arena with ease since you get very close to try to do as many hits as possible. You should buy a calibur for 2000 crowns or so and use its charge a bit, its hard to explain with words but once you start pushing things around you'll learn how the it works. But seeing that video just go with the one that looks cooler to you since they apparently work the same with some tweaked values, even if at some point there's a difference big enough to notice (ie needing one more hit on one monster somewhere, or not pushing far enough for your situation, or pushing too far) you'll be accustomed to using your sword so it won't matter. I still see it downing the turrets in one charge solo and seems to have the ability to push monsters away from you so its okay :P