5 with Heka-haywire, in Venom.
They are a great unit, better than 5 kabalites, imho. Nice meat shield, good against all CM/CMV/Dreadnoughts (4++ makes theme a good stooper), nice drugs roll and quite good antitank skill (1 greneade throwed, 1 in CC).
Just remeber to use almost 2 squads, and use it togheter when u need.
They need a little bit of practice, but when you get it, Wyches becomes way better tham Kabalytes!
Ps: works better in support to another unit (3 Grotesques+IC?)