Big Bang Level EXP Curve

I can only really contribute one data point, cause I'm lazy.

Obviously since the highest level mob is 13x, I'm gonna skip the "my level" part, and just pick the mob which is 153 post-BB and happens to be the highest level Holy target atm.
Before BB: 33600 Skelesaurs to level, 85k hp each = 2.8 billion damage
After BB: 19300 Skelesaurs to level, 260k hp each = 5 billion damage

Then there's the change in skills and base range.
Skill: 26% higher percentage on mob attacks (ACB is 37% higher, Holy is 8% lower)
Range: 49% higher average

So on the whole, my 2.8 billion damage (present) will become 5.25 billion damage (post-BB)

Meaning if the spawn and my killing efficiency is similar, 5% faster training? It should be a little better because right now I do a fair amount of overkill.

I'll add my data point, then.

Today I train on Chief Oblivion Guardians, @ 7060 exp per kill, 583,827,855 exp tnl, so 82,695 kills to level. They have 141k hp and I 2-hit them for approximately 1000 kills/hour. About 83 hours to level.

After BB I will train on the same Chief Oblivion Guardians (after redoing all the 999 quests, oh joy), @ 7099 per kill, 365,276,774 exp tnl, so only 51,454 kills to level. However, they will have 390k hp. Unlike you, I have no idea how much more damage I'm going to be doing. 2-hit? 3-hit? 4-hit? Guess I'll just have to wait and see.