I think it's as follows -
{
Actual DI properties: capped at 100% (makes it easier to program for both PvP & PvM)
Slayer: +100%
Killer: Acts as a slayer, but for one specific creature type at that % listed.
Divine Fury: 10% DI (not sure if it falls in the item DI cap at 100%)
}
Enemy of one: Take the above, multiply it by 1.5 (for the 50% bonus). this will make 100% item DI + slayer = 200%, times 1.5, to 300% (cap)
Total of these properties is capped at +300%.
DI bonuses outside the cap: These are factored into the DISPLAYED damage for your weapon, before the numbers above are applied.
Tactics: Skill * 0.625 (or 62.5%), +5% if skill GM or higher.
Anatomy: Skill * 0.5 (or 50%), +5% if skill GM or higher.
STR: STR * 0.3 (or 30%), +5% if STR 100+
Lumberjacking (if the old formula still applies): Lumberjacking * 0.2 (or 20%), +10% if GM
I'm not sure where the honor bonus falls in for Bushido, but from what I've seen (as it's PvM only) it is +10% per step (+100% at max), and I've seen it go MUCH higher than what it should, if it is really capped with the 300% DI stuff (as stated by its description in multiple places).