Not sure how your Carnifex currently costs 150pts? Those are some expensive Toxin Sacs
If it were me i'd do something about the lonely Carnifex. Seems to much of a priority target. And the Hormagaunts being only 22 and vanilla won't do much, if at all.
Maybe something like:
Flyrant
2x Zoanthropes
50x Gaunts
Dakkafex
Dakkafex
Exocrine
Kinda light on infantry. But on a 4x4 table, where they gonna hide from the 36x S6 shots + Exocrine output? So they'd probably be too busy to shoot at the Gaunts.
But that's me.