If you really plan on making a Chaos Cowl, then yes, I'd recommend going Vog Cub. Skolver isn't quite worth it, because it has no elemental defense, and pretty much no mobs deal piercing. I'd actually recommend against a Chaos Cowl in any situation, because the low defense and weakness to literally everything are certainly not worth it for just a low damage bonus. Even on a slow, strong sword, such as Divine Avenger or Khorovod, a low would be just 25 extra damage at most, I believe.

But back on the topic of resist. What you need to be aware of is the maximum amount of resist you can get - Which is 140 points. Each Vog piece gives 35, and a full bar is 70. (And a shield is 70 aswell - Essentially, no variants at all and no trinkets, but armor/helm and a shield with resist will already get you to the resist cap once they're five star) Although a maximum fire resist variant might seem like it's 35, it's actually 25 or 30. (or decreases to that much on five stars, if the armor has fire resist naturally too?) I own a Fire resistance Maximum Vog Cub Cap, and the meter isn't completely full - It's about half a bar away from full. Not having any hard numbers is a bit annoying.

Once you reach the maximum resistance, although you're NOT given complete immunity, any further resist will not have any effect at all. Having those things in mind, it isn't really hard to figure out what path you're going to take. In general, I recommend reaching the maximum resist on fire and using an armor with elemental defense. Those are the main things to fear on T3 and endgame.