| Paraxis |
If you mean ECL, wich doesn't exist in Pathfinder I would suggest +3. I wouldn't allow it at all though getting away from monsters as playable races was a very good thing Pathfinder did. Maybe let them have it for free if only npc class levels are allowed, like aristocrat it is a drow noble after all.
| Shuriken Nekogami |
Here's what i got from it. a Monster's Challenge Rating Adjustment (for monsters or templates) is also it's effective character level adjustment. 7 for stone giants, 0 for aasimaars and 2 for vampires. every 3 class levels the monster gains, it gains a free class level that doesn't factor into it's ECL. but only a number of times equal to half it's total monstrous CR (base monster CR plus template adjustments). rounded down. Challenge ratings of 1/2 or lower are never factored into ECL.
thus a drow noble is ECL +1.