I will be talking mostly from the end game perspective.
1. Yes its worth. Whoever tells u its not, never tryed to take that talent.
2. From my point of view BIS wrist for FDK is Toskz, u can also get Bracers of the Heir from RS 10m hc if u want more atk power, but i wouldnt suggest doin that.
3. Feet from Ruby Sanctum, aka Apocalypse's Advance, give u the hit u need and far more Strength than Blood Caked Stompers. So the best option for u is to get wrist with armor penetration on it.
4. Considering u are Hit and Expertise capped and that u reached 1386+ armor penetration stat prio is this: Strength, Crit, Haste.
Reason:
Attack power from Strength will buff every attack u do,
when u Crit ur main abilities (Obliterate, Frost Strike, Howling Blast, Blood Strike) deal 245% of ur normal DMG while ur melee dmg is equal to 200% of normal when it crits,
Haste on the other hand buffs ONLY ur melee dmg, just by making u hit faster. Haste gets diminished while crit doesnt, crit will always be like double normal hit, and u can never get that much Haste for it to make a huge diference in ur DPS.
This is just my prio list, u may disagree, but this is something ive learned over the time ive been playing my DK.
5. Fallen Crusader + Razorice. U can put them as u please, some ppl say FC procs more when its in main hand, some ppl like that 5-10 extra dmg per hit from Razorice if u put it in main hand.
6. From my point of view double Havoc is bad for u. Havoc MH Bloodvenom OH.
Reason:
Bloodvenom Blade gives u Hit and Armor Penetration.
81hit from feet + 52hit from BVB + 12hit from Icewalker + 2x 10str10hit gems = 165 hit rating (5.03%). This will alow u to go DOUBLE armor penetration ring (Might of Blight + Frostbrood Sapphire Ring, or Zarithrian's Offering) and gain more Attack Power overall that will buff ur MAIN HAND DMG, more than u will lose from switching from Havoc to Bloodvenom in OFF HAND DMG. So u basicly gain more combined DMG.
7. When it comes to caps, u need 26 expertise AND only 5% hit chance + 3% hit chance from talents (total of 8% melee hit). Unless u can get spell hit capped u will miss pestilence based on RNG regardless of how many extra hit u have from 5% melee to spell hit cap AND on top of that there is RESIST part of that spell which u can NEVER avoid, its all up to RNG anyway. Going for Spell Hit Cap will result in a DPS decrease overall cos u will have to lose eather Armor Penetration/Strength or Crit in order to get more hit.
8. Only talents u should sacrifice for Blood Caked Blade are Subversion and Black Ice. Explanation below...
Now lets talk about Blood Caked Blade.
This talent is only worth going when u are Armor Penetration Capped, aka 1386-1400. In that range, the closer u are to 1386 number is better.
http://imgur.com/a/VMJYD
This is a dps run i did just now on a dummy.
Gear used for it:
http://imgur.com/a/Q1EcN 1391 armor pen
Profesions: BS + JC
DBW procs: Nothing for first 50sec of the fight for some reason > Haste > Crit
Talents used for it:
http://wotlk.openwow.com/talent#jzZG...zf0cuzAofM0hxc
As u can see BCB has 3.2% of total dmg done. Lets compare that talent to Subversion and Black Ice.
I did arround 690000 dmg that would be buffed with Black Ice. We have 3 points in BCB so that means i could buff that dmg by 6% total. 6% out of 690000dmg is 41400dmg. Blood Caked Blade did 71832dmg. If u put 2 talents from BCB to Subversion i would get 6% more crit. Lets say 6% more of my Obliterates and Blood Strike hits wer crits. That would result in 43050 more dmg from extra Obli crits and 3500 more dmg from BS crits total of 46550dmg. Again, not even close to BCB dmg.
Now, lets have 1 thing in mind. Melee hits will ALWAYS HAPPEN, no matter what u do with ur spells, in what order u cast them, how much u **** up when it comes to rotation, nothing will prevent melee hits from happening (wont count complete stop of dps cos in that case u wont be able to do Oblis, FSs, and most of ur spells). So, Blood Caked Blade will do 3% of ur total dmg ALWAYS. Sometimes less 2.5%, sometimes more 4.5%. But it will always be arround 30% of ur total successfull melee hits.
When u have those last 3 talent points left, and u got the main talents in frost and unholy tree, Blood Caked Blade is by far BEST talent u can get in order to increase ur DPS.
When it comes to gear, Toskk's Maximized Wristguards VS Bracers of the Heir, or, Frostbrood Sapphire Ring VS Zarithrian's Offering, it all comes to RNG. Sometimes Agility items will end up doin more DPS, sometimes Strenght items will end up doin more DPS. I personaly like goin for that extra crit from Toskz and Frostbrood mainly cos i only use 1/3 Subversion.
About double armor pen gear, i simply dont like Ashen ring. Sometimes it just procs in bad time. But even so, lets say that the proc is worth 100 passive atk power (considering u fully use those 10sec every time) double armor pen ring with Bloodvenom will end up giving u more DMG, mainly cos Havoc gives Haste. I consider Haste a **** stat for FDK. As explained it only buffs melee white hits, and not by much tbh. Some might say that it also buffs Necrosis and BcB if u have it, but in the end, Haste on how i see it, is still a **** stat.