Are my XP formulas (or the wiki's) off?
 

So - since hitting level 58 I've hunted exclusively on Dragoon Szorn (level 45 mob) in Lesser Faydark solo as an Iksar Necromancer (wiki states 32% penalty, 10% class, 20% race).

At around kill number 550 (I believe it was actually 547) I hit level 59.

I just hit my 1200th kill on him last night (currently I have one full yellow to go till 60).

However, the wiki lists these formulas:

XP for level 58: 41333000
XP for level 59: 64689900

Given the XP for a mob of dark blue con or higher is supposed to be L^2 * ZEM, we can plug in the following to see how many kills should have taken me from 58 to 59:
Due to the pet's range, I don't have definite proof that all 550 kills were 100% me out damaging the pet, but I have a pretty good feeling it was (I parsed quite a few, pet never out damaged me and I use the exact same spell rotation every kill).

Question - why were the extra 200 kills needed? What am I missing? Or are the wiki formulas off for some portion of my testing?

Now, on to level 59 - having just hit kill #1200, that means I have 650 kills in level 59 of this mob (I'm counting up the kill messagse in my /log file).

Plugging in the same XP formula:
So...having exceeded 650 kills, why do I still have a full yellow to complete? (we can safely assume another 160 kills).

Hold on, back up... you killed that guy 1200 times? Are you insane?

I am about 99% sure the ZEM values are all guesses. I seem to remember someone mentioning that before. If that is true then it is possible whatever value your using for the zones ZEM is likely incorrect and causing that discrepancy.

Possibly...figured since he is one of two mobs in game with +TheDead faction and I want to do the scythe quest on my iksar it would be a good choice.

As an aside, where the wiki mentions +10 faction, that is wrong across the board (every mob I've ever tested on is capped at +1 faction a kill).

That would put lesser faydark at a 50 ZEM (instead of the standard 75) - that can't be right, given how many people level at the nybright sisters (or are they all suffering xp loss for those bronze weapons?).

Pretty much every number value on the wiki is wrong.

Xenow, using the formula here, a level 58 iksar necromancer killing level 45 mobs at a base ZEM should take approximately 554 kills to reach 59. Looks pretty accurate using your numbers. I used that site extensively in 59 on Zalea to figure out how many kills I needed for 60. EX: A level 59 ranger at 55% needs to solo about 370 level 45 mobs to level. (.55)(823) = 453. 823-453 = 370.

Yeah, don't trust any values you see for faction. That's for certain.

It seems that the Hell Multipliers for 55+ are different between that site and the wiki.

The wiki values are incorrect. They are a decent approximation though if you're below level 50.