Here is the FoF post from UO about Damage Increase:
http://www.uo.com/fof/fiveonfriday63.htmlTo state it plainly:
Damage Increase is broken into 2 separate parts:
PART ONE:
-Includes: Damage Increase modifier (on any weapon, jewelry, etc), Slayer(effectively doubles whatever your DI modifier total is so if you have 100DI on items, you'll now have 200DI against an enemy of that slayer type), Enemy of One (Equivalent to 100% DI), special moves(can't think of special increases your DI, but I guess there must be one)
-Total cap for this section is 300!
(So if you have 100DI on items, having a slayer weapon (doubles it to 200), and cast EoO (+100 again), you'll be at the 300DI cap for your sampire!)
PART TWO:
-Includes: Tactics, Anatomy, Strength,Lumberjacking
-Each is added up separately
(For example, if you were max in all of them you'd have 81.25(120 Tactics)+65(120 Anat)+30(Axe Weapon/LJ)+50(150 strength)=226.25)
Finally the two sections are added together for a Final DI Bonus %(In our example case, it would be 300+226.25=526.25%)
Then you take your Base Damage + (Base Damage * Final DI Bonus%) = Final Damage!
So if you had 40 Base Damage, with our example, you'll deal 210 Damage (before taking into account their resists)
Keep in mind, in PvP, Damage Increase is capped at 100% for Part 1
For HCI/DCI:
DCI - Max usable is 45% DCI, HOWEVER, if someone hits you with Hit Lower Defense you get -25DCI for short time!
This can be offset by having 70 DCI:
70(on suit)-25(hit lower def)=45(you're still at max)
Sames goes for HCI/hit lower attack! (Capped @ 45, HLA= -25)
SSI - Cap is 60 (Even though berserker's maul is 75 SSI, it will only swing at 60 SSI)
Any other stats you need to know, I probably know the info but you have to compile it from a few different places to find it all! (FiveOnFriday's usually have the most relevant info, but there's no easy way to search them!)