I'm currently having some problems with Belial on Nightmare, and I've decided I need to farm a bit to gain another level before tackling him again (and either get some new upgrades to drop, or farm enough gold while leveling to buy something good off the AH).
I'm looking to clear up some achievements while I'm doing it, so I'm considering farming some of the earliest areas of Act II, or possibly even late Act I, until I gain my level.
However, I would like to ensure that the monsters I am killing are the appropriate level for my character, and avoid going too far back and fighting mobs that aren't earning me some decent XP.
What is the earliest area that I can fight monsters as a level 45 while still making progress towards level 46?