I'd like to take a few minutes to discuss a testing technique that's helpful for getting detailed results. It involves the behavior of fixed damage attacks - i.e., things like Gouge, Rupture ticks, Venomous Wounds procs, etc. which always obey the same damage formulas. When you're actually testing such an attack, it will exhibit a damage range exactly one point wide - for instance, it will do 123-124 damage in practice. This is because, when the game calculated the damage for that move, it will find that it does (say) 123.4 damage. At this point, the game rounds randomly up or down based on the fractional part; in this example, it will round down 60% of the time and round up 40% of the time, so the actual average over the long term will be 123.4, but each individual attack will do either 123 or 124.
Hence, if you test once or twice and find that it does 123 damage, that's somewhat useful as it tells us that the internal damage number is between 122 and 124; but if you test until you get both values (123 and 124 in this case), it tells you that the answer is between 123 and 124, which basically halves the uncertainty.
Note that this is true for both crits and hits; for instance, if you look at the second Venomous Wounds test, we know both that the base damage is between 1002 and 1003, and that 1.545 times the base damage is between 1548 and 1549, which lets us state with absolute confidence that the actual damage number is between 1002 and 1002.59, which is better still. Hence, when testing this sort of thing, the most descriptive answer you can possible give is to get both damage number for both crits and noncrits; this gives us the most possible confidence in the answer.
However, sometimes the value comes out very very close to an actual damage number; for instance, in the first Venomous Wounds test above, the expected damage is 1.2 * 1.2 * 1.08 * (302.5+.1125*4347) = 1230.99912 damage. Hence, 99.9% of the time, it's going to do 1231 damage, meaning you can beat on the dummy all day and not see a 1230 - you'll note that he did 53 trials and all did the same amount. And while 53 tests with venomous wounds isn't that hard to do, once you start testing with Gouge... you won't *always* be able to get both numbers for a given attack. However, if you can at least make a reasonable effort to get them - 6 or 8 trials of a given attack - that does help reduce the uncertainty involved. More is of course better, but we'll take what we can get.
I bring this up because while ieatpaperbag's testing in post 23 is indicative that target armor is about 11950, I think it would be good to narrow it down further; in particular, some testing with a fixed-damage attack (gouge for rogues - other classes have other options) would be very helpful towards pinpointing the actual value.
Regarding Potent Poisons and Vile Poisons stacking, testing with instant poison suggests that they stack additive.
Average of around 250 instant poison hits with:
With no talent spec: 797
20% from Vile Poisons: 952
20% from Vile Poisons and 20% from Mastery: 1104.
It is also worth noting that Envenom doesn't benefit from Mastery directly.
Interesting - particularly since Venomous Wounds implies the opposite. I wonder if the damage range on IP is dirtying the results? Regardless, we'll need more testing - we should probably look at WP and DP in addition to Venomous Wounds and IP to try to get the full picture. As a note to people testing this: beware of Master Poisoner.
It looks like existing DoTs are not boosted by the 20% KSp damage buff. In this test I ruptured and swapped to a weapon with no DP on it just before a KSp.
Interesting. Could you also confirm with Rupture, and perhaps try refreshing DP during KSp? That is, if you have a rolling DP stack and refresh it during KSp, does the following tick do 20% more damage? This will, of course, require getting lucky on poison procs during a KSp, and quickly unequipping your DP weapon once it ends, but I'd be interested to know the answer.
I suppose while we're at it it might be worth verifying the behavior of poison and Venomous wound procs during KSp; I recommend Wound Poison rather than IP for testing this to avoid the IP damage range problems. And I suppose if we're being picky I'm not sure we've ever verified that autoattack damage gets boosted during KSp - we've always sort of assumed it does, but it might be good to check.