Carnage isn't worth 6 points, IMO, but then I think Vorcha Sentinel is far and away superior to Soldier. I assume you're working on a 200 wave challenge, to which I can only say good luck! We're all counting on you.
I found, with the soldier, it was best to alternate short bursts of flamer with a gun. Detonating with carnage hits your cooldowns pretty hard so I only did it on clusters or bosses. Bloodlust keeps you survivable, repeated flamer -> gun -> flamer stacks worked out very well. You could also go melee spec and use flamer to start an attack, cancel it with a heavy melee, reapply flamer, cancel with another heavy melee...
Whatever works. I used a pistol or SMG because of that sweet sweet power amp weapon mod.
I found, with the soldier, it was best to alternate short bursts of flamer with a gun. Detonating with carnage hits your cooldowns pretty hard so I only did it on clusters or bosses. Bloodlust keeps you survivable, repeated flamer -> gun -> flamer stacks worked out very well. You could also go melee spec and use flamer to start an attack, cancel it with a heavy melee, reapply flamer, cancel with another heavy melee...
Whatever works. I used a pistol or SMG because of that sweet sweet power amp weapon mod.