I'll add another vote to the tervigon. I started running an almost identical list to this, then found that I wanted more troops, objective holders, a more effective hormagaunt screen, and more back-midfield synapse. The tervigon fulfills all of these roles (giving catalyst to the gaunts).
I like the biovores, and have always found them useful. I don't play against MEQ much though, usually eldar and tau.
The devourergaunt/spore option is also good. I never found the points for more than 10 in the spore, but that seems to be enough to send them in against a backfield objective sitter team like rangers or fire warriors.
Consider ymgarls. I know you don't have elite slots free (I only use one squad of hive guard, so I have space), but I find them worth their weight, and more predictable than outflanking stealers.
