What I mean is, if I am 100 and fully perked in illusion, using the highest level spells, is there a point where making enemies rage out on each other will stop working?

There is no enemy in vanilla Skyrim that is leveled higher than 51, as far as I know. Dragons are immune, but all other enemies are affected provided you have the Master of the Mind perk. You don't even need to use the master spells. http://www.uesp.net/wiki/Skyrim_talk:Illusion#.22Higher_Level_Opponents.22