game mechanics questions (important for a marauder)

Hi,

im playing POE for few weeks and find this game realy addicting. I gained much knowledge by experience but there are still few issues that i cant understand as good as id like and i need this knowledge to develop my char knowingly. Ive read the game mechanics thread but still cant find full answers.

1. Armor efficiency.

I based on "newbie friendly GS Marauder build" made by ninjaarabstrategist and generally i find everything he wrote there to be truth. Therefore i treat health as more important than armor in terms of my defence (having elem. res. maxed of course).

1.1 How does my armor affect my damage reduction (phys and elem.) and which factors decides if a hit dealt to me wil go through my armor and make it useless? Ive seen description in game mechanics thread but im not fully satisfied with the description ive read.

2.2 Actually i have about 50% phys dmg reduction and maxed resists. It means that a mob dealing 2000 dmg (1000phys , 1000 fire) will deal 500 phys and 250 fire to me?

2. Physical damage multiplier

I deal phys damage only and now its about 8000 dps using groundslam. Obviously taking a passive nod which increase my mace dmg by 10% wont increase my dmg by 800. Let say i use marohi erqi which deals 370-570 dmg and my attack speed is 2. I wont have 740-1140 dps. Of course i would have it much higher. Therefore few questions below.

2.1. Does it increase my weapon dmg only which is then further multiplied by other multipliers (what are the rules in that?)?
2.2. "Increased mace damage" is something in principle worse than "increased physical damage" because it is not multiplied as much as "increased physical dmg"?
2.3. Same with "adds physical damage". How does it affect my dps in practice.
2.4 Is there any pattern in that matter that can be useful when deciding to buy a weapon? In fact i use marohi erqi which is great and sucks at the same time (+AOE, DMG, stun dur., - speed) and i have problems deciding if particular weapon will give me higher dps or not and i need to decide before spending few ex on a weapon.

Thanks for any answers and im sure more question will aprear.

Anyone?:)

1. good

1.1. read this http://pathofexile.gamepedia.com/Armour
that also applies to your dmg, more phy dmg you do in a single hit, it will "penetrate" more of the enemy armor and be more effective, even if the dps tooltip stays the same compared to the faster weapon.

1.2. no, phy dmg taken must be calculated (see above), fire dmg taken is correct

2. increases are additive, "more" multiplies

2.2 they are additive

2.3. a lot, it adds flat phy dmg to your weapon dmg that is then further boosted by increases and multiplies. more dps boost on fast weapons, less on slow

2.4. read 1.1., some builds depend on single hard hit and attack speed is not primary stat, flicker for example.