That's a hard question to answer, because it depends on the HP and affects the players have. The typical 'sanctuary' affect cuts damage taken by one half, so above the level where it can be assumed a player would have it, Builders tend to double the mob's damage values. This means players that don't have 'sanc' are skunked.
Long ago, Lotus of Dizzy suggested "(level divided by 2) + 5" as a guide for the mob's damage dice. Weapons should be the same, and if a mob wields a weapon, then the mob's dam should be much less so there's a difference if it's disarmed.
I suggest dropping by the DizzyMUD home page, and clicking on "Building Guide". It's not perfect, but at least it covers all the bases.http://www.dizzymud.com/
Fallon's Law: The key to balance in a MUD lies in realizing that the player's abilities follow a Bell curve - if the MUD is balanced for the average player, then a good player will be able to rip it up. If you 'fix' it so no one can advance too quickly, then players on the bottom half of the curve will be totally frustrated.
Hope that helps some,