At that point level, lord of change and if you can drop something to take a gaunt summoner and bale windo votes.
All of that will cost you 520 points so find how to free up 190 points, give the gaunt summoner terchorus bonds, and put him up on a bale wind vortex. If you make the Lord of change your HQ the gaunt summoner get a +1 to Casta, +1 from the vortex, +1 from the families ( they are free take them) so you can now cast bonds with no issues,. The gaunt summoners range then doubles to 36" for his tzeentzch fire Strom which is one of the most powerful anti horde spells in the game. Casting value of 8(5 with your +3) roll a dice for each model in the unit, on a 4+ it takes a mortal wound. I was one shottint entire 40 man rat blobs a turn. The vortex makes him safe from melee and bonds makes it so he can pass off range spells, plus vortex makes him a sniper.
lord of change can crap put a devestating spell to Merc strong single units, give him the rod and keep him at range.
Just my options, get rid of Magister, he is crap, unless you need him for a batalion, otherwise replace him with a gaunt summoner. I'd you can take a cursling as well, he dispell is nasty since you can cast instantly what ever you deny.