To make a good custom NPC it must be tested in my humble opinion. Even just changing one power can completely overpower/underpower a custom. Any EB/AV is generally a challenge just because they are at that rank. Really you just have to get out there and test it each time you change it and see what happened. Unless you are psychic 
I had joined an AE PUG in the midst of a mission and they were having an interesting discussion. the mish owner was wondering if he can make a Demon MM(only whip) a viable threat at an EB or AV level if he was given full MA, SR or other offensive powers.
Is this possible?