How fast do you want your primes and warriors to get into get to combat? If you're going to be adding deathspitters and venom cannons and losing the extra scything talons they may fall prey to being jack of all trades, master of none. They will of course throw out extra firepower but without running they will be attracting more firepower in later turns when unengaged in combat.
The warriors will need the primes to avoid insta-death from strength 8 and 9 weaponry as well as benefitting from the improved BS and WS. However, venomthropes would benefit from the same anti-insta-death cover from the prime. Have you thought about making the warriors into a brood of four or five and having one prime in with them and one prime in with three venomthropes. This will also allow you an extra elites slot (Ymgarl stealers and hive guard?)
