One of the fastest leveling spots for postgame grinding appears to be at Mt. Corus, down on the 3rd level. It's a small map and you start with the enemy right smack in front of you -- hardly any walking required.
Previously I actually loitered around the original Gaer Village location but the enemies seemed stuck at level 55 and you still had to navigate around the huge rectangular chunk of impassable terrain in the middle. The tree-type casters also tended to get lucky shots against my job-changed level 1 mercs. The Mt Corus spot on the other hand is often pretty much a straightforward melee brawl -- any nukers you bring along will have a field day.
