A good old Tyranid Swarm seems like a good way to go as people have difficulty dealing with the spawned Gaunts from my Tervigon when they have support from Venomthropes, the Hive Tyrants Old Adversary power (giving them preferred enemy) and the Tervigon giving them Feel no Pain. So if they have problems with 20 Gaunts, think about the problems of 90+ Gaunts, all with the above benefits but preferred enemy. The Hive Tyrant was just to expensive for what it does and the arms keep falling apart.
3 Hive Guard
If I want I can also swap out one unit of Termagaunts and Onslaught for my beloved Shrikes with their Boneswords/Lash Whip and Toxin Sacs. This will give me more anti-MeQ ability at the cost of some durability. After the Tervigons spawn I will easily have 120 Gaunts in 2 turns if not more. That will flood the board.
I will however need to build and paint all of those Gaunts which will take forever but should be worth it. Thank goodness I have a simple paint scheme.