Heavy armor penalties and combat speed observations
So I've been asking around in the recent week about game mechanics and ended up rather dissatisfied with the clarity I have got as a result, so I've decided to run some tests of my own.
Above is the results of some practical measurements I've taken (it's not the entire datasheet, it's too big and boring so I've picked only interesting stuff to show here). This was done on a fairly end-game character with high stats (92 Str, 74 Dex, 70 Melee, 38 Hackers), although a bit lacking in the weapon skill due to the recent swap from katanas to hackers.
Methodology was simple: I put on the stated armor pieces, and hit a 88 Toughness Elder Beak thing I have confined to the bed to be used as a testing dummy. While attacking I would pause the game and take a reading from Str and Dex tooltips, since that seems to be the only time when their readings are reflective of reality. The remaining armor slots (when not stated otherwise) were filled with my normal gear that had no relevant buffs or penalties - samurai clothpants, dark leather shirt, paladin's heavy hachigane. Pants in the spreadsheet are Samurai Legplates. Everything was Masterwork quality, weapon was a Meitou Combat Cleaver. I have also conducted a video recorded test where I have counted the frames between landing the first attack and the second, those I've only done for the slowest and fastest loadouts.
Now, the findings.
Damage: it appears that Samurai armor damage penalty is much worse than whatever you get from Holy/Unholy armor Dex penalty. Holy armor has consistently outperformed Samurai in terms of raw damage values on both the specified hacker, and also Nodachi (I did a test with it as control, since it scales purely with Dex). The difference was rather large, with damage loss being about 17% going down from Assassins rags, while Holy armor only resulted in about 9.5% damage loss. Chain shirts and mail (blackened were used) resulted in an insignificant damage reduction compared to the armor.
Conclusion: armor certainly has effect on damage, with the difference between the most damage buffing combo and most damage debuffing combo being about 19% which is substantial. That said, chain shirts don't seem to have a drastic effect, the difference being about 1-2% at most.
Attack speed: surprisingly it wasn't as bad as I thought. With the given stat it took me both Assassin's rags and wooden sandals (sandals were mostly left out of the main test) to reach the attack speed cap of 1.2, but that said - the slowest combo was 0.83 speed which was only a 30% reduction. Which in my frame counting test amounted to about 21% slower time between 2 instances of damage (alternatively, a string of 4 attacks took 1:48 longer to complete). And that's a comparison between the two extremes (as far as gear is considered that is). I'm willing to speculate that Dexterity increasing arms may make this difference even less, but I will do additional testing for that when I lose my arms :P
Conclusion: actually, it turns out that holy armor is very comparable to samurai armor+legplates combo in terms of resulting attack speed. Now yes, it's both armor and legplates versus just the holy chestplate, but I think it's a reasonable comparison due to the difference in coverage - samurai pieces don't guarantee stomach coverage even combined together, so you can still take a hit to your stomach that will only be mitigated by your shirt, while Holy plate guarantees mitigation while also providing some leg coverage. Given this, I think a reasonable combo is Holy plate+samurai clothpants to still get full leg coverage (albeit weaker) and a chance for extra stomach coverage. It doesn't help that samurai legplates have atrocious clipping issues with the holy chestplate, which is unacceptable and not worth any statistical gains.
Block Speed: now this was the least expected part, which in retrospect makes a lot of sense. The difference here was a lot more pronounced with nearly 42% difference between the fastest and the slowest. Unfortunately I didn't have means to/desire to perform a frame counting test, so all I have here is the reported numbers from Dex tooltip. This is also where the Dex maluses really show themselves, as can be seen in the difference between the Holy plate and Samurai armor+pants. While having the same attack speed, Holy manages to lose even more block speed, with a considerable difference of 1 unit between the "heavy tank" loadout with samurai armor and Assassins rags. That said, the difference between samurai set and holy plate is just 0.3, whatever that amounts to.
Conclusion: depending on how these values translate into combat situation this can be huge or meh. it's hard to tell without practical data. On paper the 42% difference looks significant. At the same time, this is also where the biggest hurt from chainmail shows, although chain shirt is quite a bit less pronounced unless stacked together with other penalties.
Overall observations: I think this goes to show that while there is a difference in performance between these, it's not as massive as one would think. Holy plate has a damage edge over samurai armor, while providing better coverage at the expense of worse blocking. Assassin rags are not that much far ahead of Holy plate damage numbers, but of course considerably ahead in terms of speed for both attack and defense. The only question there is if this speed is enough to make up for basically no protection. Chain shirt can be used with the rags at a modest decrease in performance for a 9% boost to cut damage resistance and 10% more cut resistance efficiency. I'd definitely say that chain is not worth it with Holy plate, since it already provides a considerable damage reduction to vital areas, leaving shirt to just pick up the leftover bleedthrough. That said, I'd say there's more of a case to be made for chain when using samurai armor and rags both - samurai combo only guaranteeing chest protection, while leaving stomach with 85% and 50% chance from chest and pants (and that's why you kind of need the samurai legplates with it), so your shirt would be the only reliable layer of protection on your stomach. It does further tank your speeds, but not as drastically as going from rags to heavy armor. Rags, in turn, provide merely 25% chest and 50% stomach coverage, which is even worse. Have they had at least 100% chest protection, legplates would be the obvious choice, but you have to make up for that gap or just embrace being a glass cannon. The malus for wearing a modest chain shirt doesn't seem to be too harsh as long as you don't add more of them, so perhaps it's not the worst play unless those minor speed differences make you untouchable.
TL;DR: Out of the 2 heavy armors compared, Samurai is the worst for offensive capability, Holy/Unholy is actually pretty good but potentially worse for preventing hits via blocking (but better for mitigating damage). Chain shirts are not the end of the world when used alone, and there's not a big gap between shirt and mail when you do decide to use them so go with whichever makes more sense to you. Probably don't use them with the Holy plate though. Assassin rags are considerably faster and more damaging than both heavy armors but tell me something I didn't know.