I found that wracks works just fine and its not uncommon for them to out perform my wych units. I do run a Close Combat list though and have a unit of wrack to support each wych unit.
I usually run 8 per unit and only upgrade is acothyst, I seldom miss not having ranged weapons and with furious charge they can easily glance most vehicles to death. Actually a combo charge with two wracks units against one unit can be really nasty when you get to RR wounds. I've taken out terminator squads in 1 CC phase doing that.
I have tried running wracks in venoms but found that to be less then optimal, venoms work better with a shooty unit on them so they can hang back a bit and shoot. With wracks on them you want to get close and assault and the venoms die much easier then.
5 warriors with a blaster is a nice and cheap venom crew, that actually do more than what one would think.
Assault units need Grissly Trophies on their transports so they don't break if they mess up that crucial first round of combat and then get shot up.
I hardly ever use Nightshields anymore, but I always take flicker field on my wych transports even if they get a jink save. Because wyches can not afford to be shot down, also its nice to have a vehicle save if the raider get assaulted wich happens quite often when you deliver CC units. Because it really helps to have raiders alive at the end of the game.
and now I lost my train of thought............ ..............
