Yes, i bought an affinity booster. First and last one too.
The Penta is a ballistic grenade launcher with high damage detonates on command.
Anyway, i spotted an "Assassination" alert but it turned out to be a mobile defense mission instead, but my Penta held through the whole game. With my Catalyst (no forma) build here, i was getting 2,861 damage on most of the light Infested, and 5723 damage on the Ancients....i think. I'm not quite sure which was which but chargers were the smaller damage regardless.
Due to being mostly Viral damage with only 1/3 of it Fire, you can achieve much higher damage with a Forma to increase fire damage. Viral damage is excellent for infested as it reduces their total HP for a moment, letting you kill them much easier.