This will be a prety hard hitting list for 750 pt games. I would drop warp blast from the flyrant, and give him toxin sacs - wounding those smurfs on 2+ instead of 3+ can make a huge difference
What I would consider doing is dropping a dakkafex (or devilfex as you call it), and the zoanthrope in favor of a gunfex. Dakkafexes can have a chance at glancing those dreads, but it won't be super reliable, and you'll have to rely on close combat if your opponent brings a predator, or landraider (why they would at 750, I don't know)
otherwise.. nice list, I think.