I'm thinking either the assault or tactical doctrine, but not sure which would ultimately be better. Blood Angels is Assault with+1 attack in the first round of combat...So scratch that possibility for GK, but would could ours be?
I'm hoping Tactical, as the weight of low quality fire power GK puts out would benefit the most from staying in Tac. Doctrine - however since every GK has a melee weapon I feel it's more likely that it would be in the Assault Doctrine.
I hope I'm wrong, as only getting your benefit T3 onwards is bad in a game that's often decided in the first 2 turns - but it seems more likely to me.